Display "README" with markdown style on Github

The file "README" is a markdown file but as it doesn't have the suffix
".md", Github doesn't render it with markdown style.

Rename the symlink "README" in order to be displayed with markdown style
on Github. Also, tell Automake not to look for a file called "README".

Signed-off-by: Crístian Viana <vianac@linux.vnet.ibm.com>