* Move OSC first as neutron CLI is deprecated
* Add more information on OSC usage (links to embeded command list
and the mapping guide)
* Add deprecation notice for neutron CLI
This commit also makes toctree structure simpler
At now, we have two index page unlinked from the top page.
I thought it is good first, but it potentially makes things tricky.
Let's remove such tweaks for easy maintenance.
Change-Id: I7fd79f465fa6c04bf5b13f6578796d4c2d01edfd
c4ec6759b6