docs: update group docs with new screenshots and requirements for users (#1910)

website/docs/how-to/how-to-create-and-manage-user-groups.md

@@ -50,13 +50,13 @@ This guide takes you through how to use user groups to manage permissions on you
 
 ![The groups page shown with the add user button highlighted.](/img/add-user-to-group-step-1.png)
 
-6. Find the user you'd like to add to the group add them.
+6. Find the user you'd like to add to the group and select them.
 
 ![The groups page shown with a user selected.](/img/add-user-to-group-step-2.png)
 
-7. Assign the user a role in the group and save the group. Remember that every group needs to have _at least_ one owner.
+7. Review the group users and save when you're happy.
 
-![The groups page shown with the user role highlighted.](/img/add-user-to-group-step-3.png)
+![The edit groups page shown with the save button highlighted.](/img/add-user-to-group-step-3.png)
 
 ## Assigning groups to projects
 

website/docs/user_guide/rbac.md

@@ -66,7 +66,7 @@ A user group consists of the following:
 
 - a **name** (required)
 - a **description** (optional)
-- one or more users. At least one user must have the owner role
+- a list of users (optional)
 
 Groups do nothing on their own. They must be given a role on a project to assign permissions.