git instructions

Since some time back, we have deployed the git server side http handler on
git.postgresql.org, so the instructions currently on the site are incorrect
in saying that git:// is faster than https://. In fact, we have some
reports and testing that https:// can be significantly faster (due to other
reasons). https is also a protocol that's a lot less likely to run into
firewall issues etc.

Based on that, I propose the following patch which both moves https:// up
to being the first-hand choice for protocol, and removes the references to
it being slower.

Thoughts?

--
Magnus Hagander
Me: https://www.hagander.net/ <http://www.hagander.net/>
Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>