doc: man-page for cls

Provide a man-page for the cls command.

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

doc/usage/cmd/cls.rst

@@ -0,0 +1,26 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+cls command
+===========
+
+Synopsis
+--------
+
+::
+
+    cls
+
+Description
+-----------
+
+The cls command clears the screen.
+
+Configuration
+-------------
+
+The cls command is only available if CONFIG_CMD_CLS=y.
+
+Return value
+------------
+
+The return value $? is 0 (true) on success and 1 (false) on failure.

doc/usage/index.rst

@@ -32,6 +32,7 @@ Shell commands
    cmd/button
    cmd/bootz
    cmd/cbsysinfo
+   cmd/cls
    cmd/conitrace
    cmd/cyclic
    cmd/dm