patman: Add documentation to doc/

Link to patman's documentation from the doc/ directory so that it appears
in the 'make htmldocs' output.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

doc/develop/index.rst

@@ -14,6 +14,7 @@ General
    process
    release_cycle
    system_configuration
+   sending_patches
 
 Implementation
 --------------

doc/develop/patman.rst

@@ -0,0 +1 @@
+../../tools/patman/patman.rst

doc/develop/sending_patches.rst

@@ -0,0 +1,16 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Sending patches
+===============
+
+.. toctree::
+   :maxdepth: 2
+
+   patman
+
+
+You can use a tool called patman to prepare, check and sent patches. It creates
+change logs, cover letters and patch notes. It also simplified the process of
+sending multiple versions of a series.
+
+See more details at :doc:`patman`.