Update documentation for developing a plugin locally.

[eapearson]

This will be in the newly revamped GitHub Pages documentation.
To clarify - this is regarding working on an existing plugin, getting those changes integrated into kbase-ui.

[eapearson]

@dauglyon I've copied over the old "how to update a plugin" doc, tried to catch all of the changes.
I'll revisit it again and continue with the other parts of that workflow.

https://kbase.github.io/kbase-ui/workflows/updating-a-plugin/setting-up