Rename to CONTRIBUTING.rst

This makes the GitHub interface aware of the contribution guidelines,
so it will be displayed to contributors when they submit issues or
pull requests.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
create bgp directory

Signed-off-by: ISHIDA Wataru <ishida.wataru@lab.ntt.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>