Add README for textmate plugin

plugins/textmate/README.md

+# TextMate plugin
+
+The plugin adds aliases for the [TextMate](https://macromates.com) editor.
+
+To use it, add `textmate` to the plugins array of your zshrc file:
+```
+plugins=(... textmate)
+```
+
+## Aliases
+
+| Alias           | Command     | Description   |
+|-----------------|-------------|---------------|
+| tm              | `mate .`    | Open TextMate in the current directory. |
+| tm \<directory> | `mate <directory>` `cd <directory>` | Open TextMate in the given directory and cd to it. |
+| tm <*>          | `mate "$@"` | Pass all arguments to `mate`. This allows for easy opening of multiple files. |