doc/usage: Add a reference to General rules for commands

For clarity, add a reference link to the start of the section on command
documentation that all commands follow some general rules.

Signed-off-by: Tom Rini <trini@konsulko.com>

diff --git a/doc/usage/index.rst b/doc/usage/index.rst
index 5dbc0fc..6f477b8 100644 (file)
--- a/doc/usage/index.rst
+++ b/doc/usage/index.rst
@@ -21,6 +21,9 @@ Use U-Boot
 Shell commands
 --------------
 
+For all commands in U-Boot there are some :ref:`usage/cmdline:General rules`
+that apply.
+
 .. toctree::
    :maxdepth: 1
    :glob: