[PATCH ?next?] gpio: sim: add doc file to index file

[Randy Dunlap <rdunlap@xxxxxxxxxxxxx>]

Include the gpio-sim.rst file in the GPIO index (toc/table of contents).

Quietens this doc build warning:

Documentation/admin-guide/gpio/gpio-sim.rst: WARNING: document isn't included in any toctree

Fixes: b48f6b466e44 ("gpio: sim: new testing module")
Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
---
 Documentation/admin-guide/gpio/index.rst |    1 +
 1 file changed, 1 insertion(+)

--- linux-next-20220121.orig/Documentation/admin-guide/gpio/index.rst
+++ linux-next-20220121/Documentation/admin-guide/gpio/index.rst
@@ -10,6 +10,7 @@ gpio
     gpio-aggregator
     sysfs
     gpio-mockup
+    gpio-sim
 
 .. only::  subproject and html