AGPL: Highlight the Affero Feature

This is a follow up to #197

A new point in the "required" section of the AGPL
highlights the difference to the plain GPL.
It states that running a network service of the software
triggers the disclose-source requirement, e.g. in SaaS use cases.

This is my personal interpretation of the paragraph 13 AGPL, IANAL.

Comments are welcome!
Use the More General "Network Use is Distribution"

thanks to @parkr !
Merge pull request #204 from ax3l/topic-agplSaaS

AGPL: Highlight the Affero Feature