Expand README file with information for new users

This change adds the following sections to the README file:

* Installation, steps needed to prepare the host in order to use the
  automation scripts
* Configutation, brief description of the most important configuration
  keys and pointing out the complete list is available using `mkcloud -h`.
* Usage, example usage to create a cloud and run tempest.
* Contributing, a short description how to contribute to this repository.

This change expands the README file to include a section about the
'installation' of the automation scripts and steps needed to prepare
the host in order to use the automation scripts.
`chkconfig` is enable/disable system services, it doesn't allow you to start/stop them. In any case `chkconfig` doesn't play well with systemd :\

```
# chkconfig -l libvirtd 

Note: This output shows SysV services only and does not include native
systemd services. SysV configuration data might be overridden by native
systemd configuration.

libvirtd: unknown service
```
I'll compact services manipulation just using `service` command, because it fallbacks to systemctl (at least in openSUSE)

```
# service libvirtd status
libvirtd.service - Virtualization daemon
   Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; enabled)
   Active: active (running) since Wed 2014-08-13 13:09:37 CEST; 6 days ago
     Docs: man:libvirtd(8)
           http://libvirt.org
 Main PID: 1651 (libvirtd)
...
```