docs: dt: submitting-patches: Add note about other project usage

In an attempt to make it more broadly known that other projects are
equal consumers / users of the device tree bindings, add a note to
submitting patches to say that extra care and consideration may need to
be taken when updating existing bindings.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Tom Rini <trini@konsulko.com>
Link: https://lore.kernel.org/r/20210910142419.5237-1-trini@konsulko.comSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/submitting-patches.rst

@@ -63,6 +63,9 @@ I. For patch submitters
      string that is matched by the driver (as in the "nvidia,tegra20-pcie"
      example above).
 
+  9) Bindings are actively used by multiple projects other than the Linux
+     Kernel, extra care and consideration may need to be taken when making changes
+     to existing bindings.
 
 II. For kernel maintainers
 ==========================