adds a new section to the main page: Get Support. This section directs users to places where they can interact directly with experts/developers/community (as opposed to the "Learn more" section where users support themselves). The options are:
join the community (Matrix: Datalad)
join the office hour (Matrix: Datalad office hour)
log an issue (new issue on github)
replaces "ask a question" link in footer with link to Office Hour matrix channel (was neurostars)
This PR:
Closes https://github.com/datalad/datalad.org/issues/133 Closes https://github.com/datalad/datalad.org/issues/131