Install & deployment documentation

* Adds a new toplevel section, in Master the CDN deployment document should be moved under setup/
* Adds installation documentation /cc @sle-odoo 
* Adds deployment documentation (very basic, will require extensions with examples) /cc @KangOl 
* Documents a few more CLI flags
* Reinstates support for `--no-xmlrpc` which didn't work anymore, for CRON-only workers (WSGI deployments)
* Removes unused fname in configmanager

Won't be there for some time, so if you've got things you want changed or reverted, do so directly. Likewise for an eventual merge.
Add a `warning` to tell it's does not works as expected in multiprocess mode as the each worker will try to do the rotation, leading to log lost.