doc/getting_started.rst: document GPG and NickAuth
.travis.yml: disable email notifications

and enable fast-finish even if it might not be needed yet, but it can be
helpful in the future if we add more builds.
Merge pull request #10 from Mkaysi/getting_started

doc/getting_started.rst: document GPG and NickAuth
Merge pull request #11 from Mkaysi/travis

.travis.yml: disable email notifications