Add a note on public contact data

Author: skade

README.md

@@ -9,9 +9,16 @@ Add Your User Group/Conference to the List
 1. Fork repository.
 2. Open *data/supporters.json* and add your name, location, 
 link and contact data.
+  - Note that contact data is optional and public, but we recommend adding some.
 3. Check if site is working locally if possible (see [setup](#setup)).
 4. Open a pull request.
 
+Why is my contact data public?
+------------------------------
+
+We encourage UG organisers to publicise contact emails and preferably phone numbers. This allows easy approaching and makes clear that contacting you should be the default, not an exception. Also, it allows contacting by direct means, instead of using a third-party-service like the meetups meetup page.
+
+The contact details are published on the CoC page itself to make clear who is responsible for handling incidents and who can be approached using which means.
 
 Additions or Changes to the Code of Conduct?
 --------------------------------------------
@@ -32,7 +39,6 @@ Do you want to translate to another language? Great! If you want to translate fr
 3. Open a pull request. We will try to find other native speakers and disscuss it there. The discussion may look like [the one for the Spanish translation](https://github.com/rubyberlin/code-of-conduct/pull/23).
 
 
-
 Setup
 -----