Put Beta label in ReST doc at very top
Put Beta label in ReST doc at very top

This is now linked from the docs site, so we need to make sure it's
clear that everything here is Beta, not 100% ready for primetime.

globusonline/globus-sdk-python,globus/globus-sdk-python,sirosen/globus-sdk-python,globus/globus-sdk-python,aaschaer/globus-sdk-python