* Change ansible-doc usage to show -a is for internal use
ansible-doc -a is for testing that documentation is sane. It should not
be used by normal users in production. The main reason for this is that
it is designed to fail if there are any undocumented modules or plugins.
This is good for testing that all plugins we ship are documented. It is
not good for end users who may have undocumented third-party plugins.
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