doc: addition of sort and limit features in doc

Fixes: https://tracker.ceph.com/issues/55121
Signed-off-by: Neeraj Pratap Singh <neesingh@redhat.com>

doc/cephfs/cephfs-top.rst

@@ -86,7 +86,12 @@ Interactive Commands
 1. m : Filesystem selection
       Displays a menu of filesystems for selection.
 
-2. q : Quit
+2. f : Fields management
+      Allows to choose/change the below options:
+      * sort:  The 's' key designates a field as the sort field.
+      * limit: The 'l' key lets you set the limit on the number of clients to be displayed.
+
+3. q : Quit
       Exit the utility if you are at the home screen (all filesystem info),
       otherwise escape back to the home screen.