No way to set workspace directories after extension has loaded

[jhnphm]

It would be a nice feature to be able to add workspace directories after the extension is loaded. Currently workspace directories have to be set in the telescope configuration before loading the extension, which is not refreshed after the extension is loaded.

[tg0h]

I think it would be good in the docs to mention that workspace directories must be set before loading the extension.

[astutecat]

I had a go at implementing a small function to allow users to do this, see #60