added docker networking config example (#819)
added docker networking config example (#819)

added docker networking config example - trying to address following issues:
https://github.com/higlass/higlass-manage/issues/34
https://github.com/higlass/higlass-docker/issues/148
@pkerpedjiev  - I did it finally! sorry for the delay.

what happened to us was, that the default docker's IP-pool `172.17.x.x` was interfering with the WiFi router - which has an IP from the same subrange.
So docker was modifying the `route` table like so:
```
172.17.0.0      0.0.0.0         255.255.0.0     U     0      0        0 docker0
172.18.1.0      0.0.0.0         255.255.255.0   U     0      0        0 br-blahblahblah
```
and then the machine running this docker would get unavailable via Wi-Fi ...
Pretty nasty issue, and a bit hard to figure out for someone unfamiliar with the networking.

This isn't very well documented on the docker side unfortunately, but the config-capabilities are there.
Here are all relevant links:
https://docs.docker.com/engine/reference/commandline/dockerd/
https://forums.docker.com/t/custom-ip-range-for-new-networks/60839
https://docs.docker.com/engine/reference/commandline/network_create/

PS
altering global docker config in `/etc/docker/daemon.json` seems like a great solution because it would restrict IP-addresses used by docker in general - useful when using `redis` and maybe some other docker-containers alongside higlass ...
The previous solution https://github.com/higlass/higlass-docker/issues/148 by adding `docker create network --subnet x.x.x.x` would not take care of all the cases

PPS
I have a feeling information like that belong more to something like `troubleshooting` section of some kind, but there is no such thing yet AFAIK
hms-dbmi/higlass,hms-dbmi/higlass,hms-dbmi/higlass,hms-dbmi/4DN_matrix-viewer,hms-dbmi/4DN_matrix-viewer,hms-dbmi/higlass,hms-dbmi/4DN_matrix-viewer