Fix typo in documentation

Fixup a typo in the README.

Signed-off-by: Andrew Grimberg <agrimberg@linuxfoundation.org>
Fixed usage of groupAttribute parameter
Fixed 'displayName' error when anonymous user access to a pad
Added displayNameAttribute parameter
Fixed error with group containing only one member
Merge pull request #3 from brenard/master

Fixed bug for anonymous user accessing pad, fixed groupAttribute parameter usage and added displayNameAttribute parameter
merged
merged upstream