README.md: Add a short purpose introduction. Add requirements, installation, contribution, releases and license sections.
Signed-off-by: Jelle van der Waa <jelle@vdwaa.nl>
Include a readme with steps how to add/remove/update a key in the keyring and how to release a new keyring version. Signed-off-by: Jelle van der Waa <jelle@vdwaa.nl>