killbill.properties: fix mainClass property

See https://github.com/killbill/killbill-hello-world-ruby-plugin/issues/1.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
db: fix typo in ddl.sql

See https://github.com/killbill/killbill-hello-world-ruby-plugin/issues/1.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
config: add example on how to connect to MySQL

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>