CONTRIBUTING: remove the subject verbs

After talking to a few people on the team we have decided that the
feat/fix/etc tags aren't adding much value. Use a simpler format
instead.
CONTRIBUTING: add a section about not emailing maintainers

Setup some expectation for etiquette.
MAINTAINERS: initial commit
updateengine: shut down on sigterm and reboot
Merge pull request #24 from jonboulle/update

updateengine: shut down on sigterm and reboot
version: bump to v0.1.5
version: bump to v0.1.5+git
updateengine: fix receiving more than one status update

Commit a2cdc597 changed a for loop into a select without providing any
other mechanism receiving multiple signals. Re-add the for. :(
updateengine: add tests for RebootNeededSignal