Added reference to publishing guideline to QA plan

Name: Stefan Rieger
Description: Added reference to publishing guideline
Gist URL: No
Cryptography: No
Author(s): Stefan Rieger
I hereby declare that I accept to contribute following the openETCS terms of use and the openETCS IP policy.

http://openetcs.org/termsofuse/

https://github.com/openETCS/ecosystem/wiki/IP-Policy