README.md: Add info about Change-type and Changelog-entry
README.md: Add info about Change-type and Changelog-entry

Change-type: patch
Changelog-entry: Document Change-type and Changelog-entry git commit footers
Signed-off-by: Andrei Gherzan <8dc7c09356db0b1762fb140617d7375c0a5a4131@resin.io>

resin-os/meta-resin,resin-os/meta-resin,resin-os/meta-resin,resin-os/meta-resin