Created "BUGS.md" which details to the Vela Community
how to issue bug report using the Maniphest Bug Tracker.
Also added a reference to it in "README.md".

Signed-off-by: erik.andersson@arm.com <erik.andersson@arm.com>
Change-Id: I0120a890c8447907e32de6b10a24eceade09df7d