Delegate management of a group to a another group

Using Sharepoint 2013 on-premises.

I have the following setting:
- a document library (DocLib)
- a group (LibReaders) which as read access to the DocLib library, but no other permissions on the site

I would like to delegate the task of adding/removing users in LibReaders to a given user (joe), but I do not want to grant joe access to other parts of the site, except to DocLib. Joe is a member of LibReaders.

I have created another group (LibReadersGroupMgrs) with no permissions, added joe to it, and set this group as the owner of group LibReaders. 

The issue is that joe cannot access the LibReaders management page (_layouts/15/User.aspx?...). What are the _minimal_ permissions that I need to grant to LibReadersGroupMgrs to let this group administer LibReaders group ?