update authenticate step to check for GITHUB_TEAM_ID
update setup instructions in readme
Merge pull request #4 from sankage/teams

update authenticate step to check for GITHUB_TEAM_ID
Expand Oauth scope to "repos".

Although we don't need "repo" access, this allows us to see non-publicized memberships, as well as team designation.

See https://github.com/benbalter/jekyll-auth/pull/4 for further discussion.

Props @sankage for much of the legwork.
relax scope back down to user