kate: add README (#7238)

plugins/kate/README.md

+# Kate plugin
+
+This plugin adds aliases for the [Kate editor](https://kate-editor.org).
+
+To use it, add kate to the plugins array of your zshrc file:
+```
+plugins=(... kate)
+```
+
+## Aliases
+
+| Alias | Command                | Description         |
+|-------|------------------------|---------------------|
+| kate  | `kate >/dev/null 2>&1` | Start kate silently |
+
+## Functions
+
+| Function   | Description                              |
+|------------|------------------------------------------|
+| `kt <dir>` | Change to directory and start kate there |