How to give a particular role, the right to register new user
I couldn't get why it's a problem, you are already there, just simply create a role "Webmaster" if you dont have one already, and give this role the same permission "Administer Users" too. but if you only want to give specific permission such as ONLY creating users you might need Administer Users by Role module


  This module allows site builders to set up fine-grained permissions
  for allowing users to edit and delete other users — more specific than
  Drupal Core's all-or-nothing 'administer users' permission. It also
  provides and enforces a 'create users' permission.
  
  To use this module:
  
  Create a role for the users who you'd like to be able to
  create/edit/delete other users Give that new role the 'administer
  users' permission and give it the desired Administer Users by Role
  permissions If the user-being-edited has multiple roles, the
  user-doing-the-editing must have permission to edit ALL of the
  user-being-edited's roles.