Rename README under GraphHammer-examples

Added ".md" extension.

Signed-off-by: Atsuro Hoshino <atsuro.hoshino@parsci.com>
Markdown heading format

Signed-off-by: Atsuro Hoshino <atsuro.hoshino@parsci.com>
Merge pull request #1 from atsurohoshino/master

Rename README under GraphHammer-examples