Add proxy access docs [skip ci]

docs/proxy.md

+# Proxy setup
+
+In case of proxy access to the internet you should setup proxy. There are three places where you need it
+
+## OS
+
+Just do 
+
+```
+export http_proxy=http://192.168.1:3128 https_proxy=http://192.168.1.1:3128 
+```
+
+Or with auth
+```
+export http_proxy=http://user:password@192.168.1:3128 https_proxy=http://user:password@192.168.1.1:3128 
+```
+
+
+After all command will get access to the net. 
+
+## Docker
+
+After docker installation docker daemon itself have to get access to internet
+```
+mkdir /etc/systemd/system/docker.service.d/
+```
+
+Place there file `/etc/systemd/system/docker.service.d/http-proxy.conf` with such content 
+```
+[Service]
+Environment="http_proxy=http://192.168.1.1:3128"
+Environment="https_proxy=http://192.168.1.1:3128"
+```
+
+then 
+
+```
+systemctl daemon-reload
+systemctl restart docker
+```
+
+## Tower
+
+Container acts as separate network node so it has to get access to internet separately. Append to  `docker-compose.yml` in `environment` section that vars
+
+```
+version: '2.1'
+services:
+  tower:
+  .....
+    environment:
+      https_proxy: http://192.168.1.1:3128
+      http_proxy: http://192.168.1.1:3128
+
+```
+
+And `docker-compose up -d`