point setup doc to 2-2-stable branch
Bumps rugged version to 0.18
Fix Checkout command to use 2.2 stable (instead of 2.0)
Merge pull request #173 from Philzen/patch-1

Fix install.md checkout command to use 2.2 tag/branch
Merge pull request #156 from alexdo/master

Bumps rugged to version 0.18.0.b1, resolving GPG issues