of12: set default attributes for group-related classes

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
of13: set default attributes for group-related classes

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
of14: set default attributes for group-related classes

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
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>