add port forwarding

README.md

@@ -21,6 +21,9 @@ services:
       - "./yggdrasil:/etc/yggdrasil"
     sysctls:
       - "net.ipv6.conf.all.disable_ipv6=0"
+    environment:
+      - BIND_PORT=80
+      - BIND_ADDRESS=nginx
 ```
 
 ## docker cli
@@ -36,3 +39,12 @@ docker run \
 yggdrasil
 ```
 
+# Parameters
+
+Container images are configured using parameters passed at runtime.
+
+|Parameter|Function|
+|:--------|:-------|
+|-e BIND_PORT|Port to forward.|
+|-e BIND_ADDRESS|Address of another docker service to forward to.|
+