New instructions on how to install from github.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@3391 44740490-163a-0410-bde0-09ae8108e29a
Fix for the recently added install instructions.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@3392 44740490-163a-0410-bde0-09ae8108e29a