Add documentation on Wezterm plugins

[alecthegeek]

What page or section of the docs have an issue?

Needs a new section?

Describe the issue

Wezterm plugins have no documentation. It would be useful to have some.

1. End user Docs.

Initially we can use paraphrse the content of the original change at e4ae8a8

However we need to add more details on how to update plugins and discover where they are located.

2. Developer Docs.

A more substantial section is also needed to explain how to setup a plugin development project.

[wez]

If you'd like to make a start on this, the way to go about it is:

• Add a Page like this to the config section of the docs:
  https://github.com/wez/wezterm/blob/2b76c63bb618d26609434c06282c8755229c4099/ci/generate-docs.py#L440C13-L440C66

eg: Page("Plugins", "config/plugins.md"),

• then create the file docs/config/plugins.md with the content.

Once you've added that entry to ci/generate-docs.py, and created the docs/config/plugins.md, you can then run the doc build locally:

$ ./ci/build-docs.sh serve

(docker is required to run that script)

That will build the docs (takes a few seconds), then run an http server and print out a URL that you can open in your browser and then navigate to your new page. As you make changes to doc files, the docs will be rebuilt and the browser will automatically reload.

[alecthegeek]

Thanks @wez . I'll give it a burl