'Provisional User' example needed to have search permissions added

otherwise the sort and group dropdowns were not populated with the
names of the properties of the issue.

See the thread titled "access control rule for Sort and Group
function" by austin.wangxu ending with:
https://sourceforge.net/p/roundup/mailman/message/36408780/

Author: rouilj

doc/customizing.txt

@@ -5050,6 +5050,12 @@ First up, we create the new Role and Permission structure in
     p = db.security.addPermission(name='View', klass='issue',
         check=own_issue, description='Can only view own issues')
     db.security.addPermissionToRole('Provisional User', p)
+    # This allows the interface to get the names of the properties
+    # in the issue. Used for selecting sorting and grouping
+    # on the index page.
+    p = db.security.addPermission(name='Search', klass='issue')
+    db.security.addPermissionToRole ('Provisional User', p)
+
 
     # Assign the Permissions for issue-related classes
     for cl in 'file', 'msg', 'query', 'keyword':