docs/vm: ksm: split userspace interface to admin-guide/mm/ksm.rst

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/mm/index.rst

@@ -23,6 +23,7 @@ the Linux memory management.
 
    hugetlbpage
    idle_page_tracking
+   ksm
    pagemap
    soft-dirty
    userfaultfd