Docker config file location on windows to, e.g., enable insecure registry / docker options

The following worked for me:

1. edit C:/Users/Username/.docker/machine/default/config.json
2. add the registry : "InsecureRegistry": ["x.x.x.x:port"]
3. restart docker (see comment below)*
4. restart windows (there must be a better way ;-)
5. docker login x.x.x.x:port