Add Welcome section to docs

* Fixes unrelated typo in readme
* Add new Welcome section with history, team, callouts, and community
subsections
* Redesigns callouts to be a bit lighterweight with colored headings
shorter avatar urls
use irc link
Merge branch 'master' into docs_welcome
Copy edits from @cvrebert and @juthilo
dat @juthilo edit
dat hash
move to separate about page
add translations, copy edit a few things, and fix alignment of ads
Merge branch 'docs_welcome'