docs: Add documentation for the project

This commit adds documentation for the project. This includes
information about the project organisation and instructions for setting
up a development environment and building the Blinky application. It
also updates README.md to provide an introduction to the project.

Miscellaneous files are also added, including the LICENSE file and
guidelines for contributing to the project.

Signed-off-by: Chuyue Luo <Chuyue.Luo@arm.com>