Move actual docs to lf-lang main repo

[axmmisaka]

This was something we thought about a while ago.

MDX Docs will be version-controlled along with lf-lang repo to ensure they are up-to-date. This website checks out docs from the repo with different tags and builds website from time to time with these docs, without containing any actual document.

Should we still proceed along this route?

[lhstrh]

Not sure it is a priority, honestly... What we have has worked pretty well, so I'm not sure it's worth the time investment.