docs: add documentation

README.md

@@ -1,6 +1,43 @@
 # opencode.nvim
 
-Prototype Neovim plugin that opens `opencode` in a terminal split on the right.
+Neovim plugin that toggles an `opencode` terminal in a right-side split.
+
+The terminal buffer is kept alive when hidden, so your `opencode` session remains
+available across toggles.
+
+## Requirements
+
+- Neovim 0.10 or newer
+- The `opencode` CLI installed and available on `$PATH`
+
+This plugin does not install or bundle `opencode`; it only starts the CLI in a
+Neovim terminal. Use of `opencode` is subject to that project's own license and
+terms.
+
+## Installation
+
+Install with your plugin manager of choice.
+
+Using `lazy.nvim`:
+
+```lua
+{
+  "agj/opencode.nvim",
+  opts = {
+    width = 0.3,
+  },
+}
+```
+
+Using `vim-plug`:
+
+```vim
+Plug 'agj/opencode.nvim'
+```
+
+```lua
+require("opencode").setup()
+```
 
 ## Usage
 
@@ -10,18 +47,46 @@ Run:
 :OpenCodeToggle
 ```
 
-The command opens `opencode` in a right-side terminal window sized to 40% of the
-screen width. Running the command again closes only the window; the terminal
-buffer and `opencode` session stay alive. Run `:OpenCodeToggle` again to show the
-same session.
+The command opens `opencode` in a right-side terminal window sized to 30% of the
+screen width by default. Running the command again closes only the window; the
+terminal buffer and `opencode` session stay alive. Run `:OpenCodeToggle` again to
+show the same session.
 
 ## Configuration
 
 ```lua
 require("opencode").setup({
-  width = 0.4,
+  width = 0.3,
 })
 ```
 
 `width` is the fraction of the screen width used by the terminal window. The
-default is `0.4`.
+default is `0.3`. It must be greater than `0` and less than or equal to `1`.
+
+## Help
+
+After installing the plugin, run:
+
+```vim
+:help opencode.nvim
+```
+
+If your plugin manager does not generate helptags automatically, run:
+
+```vim
+:helptags ALL
+```
+
+## License
+
+opencode.nvim is free software released under the GNU General Public License,
+version 3 only. See [LICENSE](LICENSE) for the full license text.
+
+This program is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+PARTICULAR PURPOSE.
+
+## Trademark Notice
+
+opencode.nvim is an independent Neovim plugin and is not affiliated with,
+endorsed by, or sponsored by the maintainers of `opencode` or Neovim.