More descriptive wording for Contact section

- Replace the subtitle that mentions they can reach out to us over
  various communication channels, with reasons why they might want to
  contact us

- We do most of our planning on GitHub, so remove "IRC" from that
  sentence

- Add icons to the various public communication channels that we use
  (looks a bit messy IMO, maybe if icons replaced the bullets?)

- Be specific about the various ways they can reach us

- Add Twitter as a communication channel

- Replace the reader's possible lack of experience, with preferring
  privacy as the reason to possibly use email