Documentation: man-page for command bootd

Provide a man-page for the bootd command.

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

doc/usage/cmd/bootd.rst

@@ -0,0 +1,38 @@
+.. SPDX-License-Identifier: GPL-2.0+:
+
+bootd command
+=============
+
+Synopsis
+--------
+
+::
+
+    bootd
+
+Description
+-----------
+
+The bootd command executes the command stored in the environment variable
+*bootcmd*, i.e. it does the same thing as *run bootcmd*.
+
+Example
+-------
+
+::
+
+    => setenv bootcmd 'echo Hello World'
+    => bootd
+    Hello World
+    => setenv bootcmd true
+    => bootd; echo $?
+    0
+    => setenv bootcmd false
+    => bootd; echo $?
+    1
+
+Return value
+------------
+
+The return value $? of the bootd command is the return value of the command in
+the environment variable *bootcmd*.

doc/usage/index.rst

@@ -23,6 +23,7 @@ Shell commands
    cmd/addrmap
    cmd/askenv
    cmd/base
+   cmd/bootd
    cmd/bootdev
    cmd/bootefi
    cmd/bootflow