Add a getting started guide
better formatting for command comparisons
lots of doc fixes
Add a proper MIT LICENSE file.

Fixes #122.
improve error message on panic
more guide fixes
remove unnecessary intro in env section
remove other install instructions
move git sha/tag column to end of description

If the git description for the release's hash is not already included in
the release's description (and thus isn't just a hash), append it to the
end of the description when we display it.

Fixes #93.