Specify a local address when exposing ports with Docker

cf. https://docs.docker.com/engine/reference/commandline/run/#publish-or-expose-port--p---expose

Signed-off-by: Richard Gibson <richard.gibson@gmail.com>

Author: gibson042

README.md

@@ -174,15 +174,15 @@ The Docker image can be used to serve element-web as a web server. The easiest w
 it is to use the prebuilt image:
 
 ```bash
-docker run -p 80:80 vectorim/element-web
+docker run -p 127.0.0.1:80:80 vectorim/element-web
 ```
 
 To supply your own custom `config.json`, map a volume to `/app/config.json`. For example,
 if your custom config was located at `/etc/element-web/config.json` then your Docker command
 would be:
 
 ```bash
-docker run -p 80:80 -v /etc/element-web/config.json:/app/config.json vectorim/element-web
+docker run -p 127.0.0.1:80:80 -v /etc/element-web/config.json:/app/config.json vectorim/element-web
 ```
 
 To build the image yourself: