Include Code of Conduct, Social Contract and Community Council links

During the last CC meeting, we discussed a few low-hanging fruits to make more public our governance documents. One of the places to publicize them is the community portal.

Include:

• Code of Conduct https://gitweb.torproject.org/community/policies.git/tree/code_of_conduct.txt
• Social Contract https://gitweb.torproject.org/community/policies.git/tree/social_contract.txt
• Community Council https://gitweb.torproject.org/community/policies.git/tree/community_council.txt

cc @ahf @pili @catalyst @gaba