update command line usage

Author: ogios

data/doc/2.cmd.md

@@ -62,3 +62,29 @@ way-edges togglepin <group_name>:<widget_name>
 ```
 
 Most of the widgets support `pin`, use `group name` + `:` + `widget name` to toggle a widget's pin state.
+
+## Shell completions
+
+### Bash
+
+If you install way-edges via [way-edges-bin](https://aur.archlinux.org/packages/way-edges-bin/), then you'll get completion script installed to `/usr/share/bash-completion/completions/way-edges`.
+
+Else then you'll have to copy the `https://github.com/way-edges/way-edges/blob/master/way-edges-bash-complete.bash` file to that place(you can rename it to `way-edges`).
+
+### Other shell
+
+For other shell, you'll have to generate it on your own:
+
+```shell
+$ COMPLETE=zsh way-edges
+```
+
+But there might be some issues generating completions after colon, you can either find a way and modify the script on your own, or submit an issue on GitHub.
+
+### _AS A REMINDER_:
+
+current clap version: 4.5.20
+current clap-complete version: 4.5.36
+
+The doc for dynamic completion is not robust(it's still in `unstable-xx` feature), it doesn't show the right way of generating dynamic completion script.  
+And also, to avoid the misbehave of completion with colon(`:`), i have to modify the completion script my own.