Add missing automodule doc for yaml_load
Add missing automodule doc for yaml_load

A previous commit added a test plugin for yaml_load, but missed
the associated doc file.

Change-Id: I5574303197bfbcdfca80f841febd25224556eede

stackforge/bandit,chair6/bandit,stackforge/bandit,pombredanne/bandit,pombredanne/bandit