Backlog/112 alarms

Adds an Alarm document, finishing the issue https://github.com/telefonicaid/fiware-connectors/issues/112

It also adds new INFO traces needed by the alarm system.

A minor fix in the README has been done as well.
This "Message types" currently is a copy of README.md same fragment? I wouldn't repeat the same in two places: diffcult and error-prone to keep in sync as modifications are needed. It's better to put the content in one place and a reference pointing to it in the other.