minor #6960 [Reference] add back the option's description (xabbuh)

This PR was merged into the 2.8 branch.

Discussion
----------

[Reference] add back the option's description

This was accidentally removed in #6908 when the deprecation warnings were added.

Commits
-------

9e56a2b add back the option's description

Author: xabbuh

reference/configuration/framework.rst

@@ -596,6 +596,8 @@ username
 
 **type**: ``string`` **default**: ``''``
 
+When needed, the username for the profiling storage.
+
 password
 ........