feat(ngrok): add completion plugin (#12826)

plugins/ngrok/README.md

@@ -0,0 +1,20 @@
+# ngrok plugin
+
+This plugin adds completion for the [ngrok](https://ngrok.com) CLI.
+
+To use it, add `ngrok` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... ngrok)
+```
+
+This plugin does not add any aliases.
+
+## Cache
+
+This plugin caches the completion script and is automatically updated asynchronously when the plugin is
+loaded, which is usually when you start up a new terminal emulator.
+
+The cache is stored at:
+
+- `$ZSH_CACHE/completions/_ngrok` completions script