docs: netlabel: convert docs to ReST and rename to *.rst

Convert netlabel documentation to ReST.

This was trivial: just add proper title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/netlabel/index.rst

@@ -0,0 +1,21 @@
+:orphan:
+
+========
+NetLabel
+========
+
+.. toctree::
+    :maxdepth: 1
+
+    introduction
+    cipso_ipv4
+    lsm_interface
+
+    draft_ietf
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`