Added doc/usage.md

Resolves #158
Resolves #103

README.md

@@ -5,6 +5,7 @@ A lightweight text editor written in Lua
 
 * **[Get lite](https://github.com/rxi/lite/releases/latest)** — Download
   for Windows and Linux
+* **[Get started](doc/usage.md)** — A quick overview on how to get started
 * **[Get plugins](https://github.com/rxi/lite-plugins)** — Add additional
   functionality
 * **[Get color themes](https://github.com/rxi/lite-colors)** — Add additional colors

doc/usage.md

@@ -0,0 +1,146 @@
+# lite
+
+![screenshot](https://user-images.githubusercontent.com/3920290/81471642-6c165880-91ea-11ea-8cd1-fae7ae8f0bc4.png)
+
+## Overview
+lite is a lightweight text editor written mostly in Lua — it aims to provide
+something practical, pretty, *small* and fast, implemented as simply as
+possible; easy to modify and extend, or to use without doing either.
+
+
+## Getting Started
+When lite is started it's typically opened with a *project directory* — this
+is the directory where your project's code and other data resides. The project
+directory is set once when lite is started and, for the duration of the
+session, cannot be changed.
+
+To open lite with a specific project directory the directory name can be passed
+as a command-line argument *(`.` can be passed to use the current directory)* or
+the directory can be dragged onto either the lite executable or a running
+instance of lite.
+
+The main way of opening files in lite is through the `core:find-file` command
+— this provides a fuzzy finder over all of the project's files and can be
+opened using the **`ctrl+p`** shortcut by default.
+
+Commands can be run using keyboard shortcuts, or by using the `core:find-command`
+command bound to **`ctrl+shift+p`** by default. For example, pressing
+`ctrl+shift+p` and typing `newdoc` then pressing `return` would open a new
+document. The current keyboard shortcut for a command can be seen to the right
+of the command name on the command finder, thus to find the shortcut for a command
+`ctrl+shift+p` can be pressed and the command name typed.
+
+
+## User Module
+lite can be configured through use of the user module. The user module can be
+used for changing options in the config module, adding additional key bindings,
+loading custom color themes, modifying the style or changing any other part of
+lite to your personal preference.
+
+The user module is loaded by lite when the application starts, after the plugins
+have been loaded.
+
+The user module can be modified by running the `core:open-user-module` command
+or otherwise directly opening the `data/user/init.lua` file.
+
+
+## Project Module
+The project module is an optional module which is loaded from the current
+project's directory when lite is started. Project modules can be useful for
+things like adding custom commands for project-specific build systems, or
+loading project-specific plugins.
+
+The project module is loaded by lite when the application starts, after both the
+plugins and user module have been loaded.
+
+The project module can be edited by running the `core:open-project-module`
+command — if the module does not exist for the current project when the
+command is run it will be created.
+
+
+## Commands
+Commands in lite are used both through the command finder (`ctrl+shift+p`) and
+by lite's keyboard shortcut system. Commands consist of 3 components:
+* **Name** — The command name in the form of `namespace:action-name`, for
+  example: `doc:select-all`
+* **Predicate** — A function that returns true if the command can be ran, for
+  example, for any document commands the predicate checks whether the active
+  view is a document
+* **Function** — The function which performs the command itself
+
+Commands can be added using the `command.add` function provided by the
+`core.command` module:
+```lua
+local core = require "core"
+local command = require "core.command"
+
+command.add("core.docview", {
+  ["doc:save"] = function()
+    core.active_view.doc:save()
+    core.log("Saved '%s', core.active_view.doc.filename)
+  end
+})
+```
+
+Commands can be performed programatically (eg. from another command or by your
+user module) by calling the `command.perform` function after requiring the
+`command` module:
+```lua
+local command = require "core.command"
+command.perform "core:quit"
+```
+
+
+## Keymap
+All keyboard shortcuts in lite are handled by the `core.keymap` module. A key
+binding in lite maps a "stroke" (eg. `ctrl+q`) to one or more commands (eg.
+`core:quit`). When the shortcut is pressed lite will iterate each command
+assigned to that key and run the *predicate function* for that command — if the
+predicate passes it stops iterating and runs the command.
+
+An example of where this used is the default binding of the `tab` key:
+``` lua
+  ["tab"] = { "command:complete", "doc:indent" },
+```
+When tab is pressed the `command:complete` command is attempted which will only
+succeed if the command-input at the bottom of the window is active. Otherwise
+the `doc:indent` command is attempted which will only succeed if we have a
+document as our active view.
+
+A new mapping can be added by your user module as follows:
+```lua
+local keymap = require "core.keymap"
+keymap.add { ["ctrl+q"] = "core:quit" }
+```
+
+
+## Plugins
+Plugins in lite are normal lua modules and are treated as such — no
+complicated plugin manager is provided, and, once a plugin is loaded, it is never
+expected be to have to unload itself.
+
+To install a plugin simply drop it in the `data/plugins` directory — installed
+plugins will be automatically loaded when lite starts. To uninstall a plugin the
+plugin file can be deleted — any plugin (including those included with lite's
+default installation) can be deleted to remove its functionality.
+
+If you want to load a plugin only under a certain circumstance (for example,
+only on a given project) the plugin can be placed somewhere other than the
+`data/plugins` directory so that it is not automatically loaded. The plugin can
+then be loaded manually as needed by using the `require` function.
+
+Plugins can be downloaded from the [plugins repository](https://github.com/rxi/lite-plugins).
+
+
+## Color Themes
+Colors themes in lite are lua modules which overwrite the color fields of lite's
+`core.style` module. Color themes should be placed in the `data/user/colors`
+directory.
+
+A color theme can be set by requiring it in your user module:
+```lua
+require "user.colors.winter"
+```
+
+Color themes can be downloaded from the [color themes repository](https://github.com/rxi/lite-colors).
+