This updates ironic's landing page https://docs.openstack.org/ironic/latest/
so that:
- it isn't only for developer documentation
- the sections are reordered to better reflect the order of information
from new user to experienced developer
- a user guide entry was added (since there is user documentation)
- the releasenotes/index.rst was removed since it was a placeholder to
redirect links to new locations. Due to the doc migrations, that original
URL doesn't exist anymore anyway, so this page should not be bookmarked
so we don't need to keep it
- the section names are more consistent
- the User Guide and Administrator Guide sections have links to subsections
- removed a link to <api/index>, which doesn't exist
Change-Id: I413048526f96a8c11eb7da365b935f617307de10
1bd81b9699