Split community page into "Community" and "Governance"

[SethTisue]

the community page is getting way too long, and these are two reasonably distinct subjects

certainly community would link to governance, probably the reverse link too

this came up at the advisory board meeting

fwiw, Rust has top level links for both:

[SethTisue]

relevant Scala Center proposal from @romanowski : https://github.com/scalacenter/advisoryboard/blob/main/proposals/030-governance-page.md

in the first round of work on that proposal we just expanded the Community page, but I suggest splitting it in this round, to make more room for the governance information that we plan to add

[SethTisue]

we could start simply by relocating the current "Governance" and "Who's behind Scala?" sections. I suggest we reverse the order on the new page

[SethTisue]

this will be fixed by https://github.com/scala/scala-lang/pull/1700