docs/vm: transhuge: split userspace bits to admin-guide/mm/transhuge

Now that the administrative information for transparent huge pages is
nicely separated, move it to its own page under the admin guide.

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/admin-guide/mm/index.rst b/Documentation/admin-guide/mm/index.rst
index a69aa69..8454be6 100644
--- a/Documentation/admin-guide/mm/index.rst
+++ b/Documentation/admin-guide/mm/index.rst
@@ -27,4 +27,5 @@
    numa_memory_policy
    pagemap
    soft-dirty
+   transhuge
    userfaultfd