Fixes several small bugs regarding #48

- Proxies are `off` by default so `SHADOWSOCKS_PASSWORD` is not required
- Documentation fixed and clarified
- `PORT_FORWARDING` should be `on` or `off` only now (although it's backward compatible with `false` and `true`)

entrypoint.sh

@@ -476,7 +476,7 @@ fi
 # READ FORWARDED PORT
 ############################################
 
-if [ "$PORT_FORWARDING" == "true" ]; then
+if [ "$PORT_FORWARDING" == "on" ]; then
   sleep 10 && /portforward.sh &
 fi