Create grefrath.json

[deichy]

No description provided.

[christian-weiss]

URL of Grefrath is: http://freifunk-grefrath.de
As we can see in Community Directory https://github.com/freifunk/directory.api.freifunk.net/blob/master/directory.json#L122 that Community API file for Grefrath is no longer hosted at github. Community Directory points to: http://freifunk-grefrath.de/FreifunkGrefrath-api.json

I think this PR is obsolete and should be closed.

Please see my comment in #17
Feel free to create Issues and Pull Requestes to https://github.com/Freifunk-Hamm/ffapi if you want to change other Community API files in the future.