Document the langserver situation

[Akuli]

Should document:

• what is a langserver, why we need them, what problem do they solve
• what langservers does Porcupine come with by default
• how are langservers configured in porcupine
• which langserver we use for Python and why (some options: pyls, pylsp, pyright, basedpyright)
• how to look at JSON messages that langserver sends/receives with porcupine (very noisy!)
• probably some other stuff that doesn't come to mind right now

Some of this might already be in the wiki. Because nobody reads the wiki, we should at least move those docs out of the wiki if not rewrite/update them.