Add hypervisor information on README.md.

No information was available about how kimchi is run and which are the
supported hypervisors.

Signed-off-by: Christy Perez <christy@linux.vnet.ibm.com>
Limit README.md to 80 columns.

Make the file easier to read.
Add mailing list information.

It was impossible for a new developer to figure out where to send
patches to without this information.