Make it clear that limiting search and mention does only work when nickname is filled in

Problem
On the profile privacy settings page (/admin/config/people/social-profile) it is not clear that the setting to "Limit search and mention" only has effect on people who actually filled in their nickname.

This is the current description for this setting.

Enabling this setting causes users' full name to be hidden on the platform. Users with the '%display_name' permission will still see the full name whenever available. Only users with the '%search_name' permission will find users using their full name through search or mentions.

Solution
Let's change the description text to make this clearer:

Enabling this setting causes users' full name to be hidden on the platform when the user has filled in their nickname. This setting won't hide the full name of users who didn't fill in a nickname. Users with the '%display_name' permission will still see the full name whenever available. Only users with the '%search_name' permission will find users using their full name through search or mentions.