Remove ref to salt/modules in module writing docs

A beginner is not going to know what this means, so don't muddy the
waters with this info. Besides, new modules should only go in
salt/modules once they are accepted into salt proper. Custom modules
should pretty much always go into _modules.
Add ref/tops/all/salt.tops.reclass_adapter.rst

auto-gen'ed rst file for new reclass adapter
Merge pull request #6223 from terminalmage/docs

Remove ref to salt/modules in module writing docs