Improve documentation on permissions

Zendesk issue: https://gitlab.zendesk.com/agent/tickets/26323

Documentation should be added to show that a master can only add new members to a group project not the group itself

Update

@stanhu @MrChrisW

I closed this ticket with our proposed Just In Time Documentation workflow that adds this to a list of issues whose documentation needs to be worked on but wasn't picked up.

Notes for this workflow can be found on our Support Team Call dated: Friday 2016-06-10

@axil Let me know if this can be expedited as it has been pending for quite a while.