chore: some doc on extenstions

README.md

@@ -30,6 +30,8 @@ Head over to the [release page](https://github.com/mterm-io/mterm/releases/lates
 mterm is customizable in a few ways -
 - add your own [commands](#commands) to the terminal
   - quick add a command with `:cmd command_name` and edit this
+- add extensions to the terminal
+  - quick add an extension with `ext add mterm-red`, see [extensions](./docs/extensions.md) for more info
 - change the [theme](#theme) of the terminal
   - quick change the theme with `:theme` or `:css`
 - change the [settings](#settings) of the terminal

docs/extensions.md

@@ -0,0 +1,17 @@
+## Known Extensions
+
+> Please make a pull request to add your extension to this list
+
+- [mterm-ext-red](#mterm-ext-red)
+- more...
+
+
+### mterm-ext-red
+
+```bash
+ext add mterm-red
+```
+Make your terminal (mterm) red 10 seconds -
+
+![red terminal](https://github.com/mterm-io/mterm-ext-red/blob/HEAD/info.png?raw=true)
+