Add ARGS env variable to alpine Dockerfile (#1537)

docker/alpine/Dockerfile

@@ -15,6 +15,7 @@ ENV METHOD      aes-256-cfb
 ENV TIMEOUT     300
 ENV DNS_ADDR    8.8.8.8
 ENV DNS_ADDR_2  8.8.4.4
+ENV ARGS=
 
 RUN set -ex && \
     apk add --no-cache --virtual .build-deps \
@@ -58,4 +59,5 @@ CMD ss-server -s $SERVER_ADDR \
               --fast-open \
               -d $DNS_ADDR \
               -d $DNS_ADDR_2 \
-              -u
+              -u \
+              $ARGS

docker/alpine/README.md

@@ -32,6 +32,7 @@ $ docker ps
 ```
 
 > :warning: Click [here][6] to generate a strong password to protect your server.
+> You can use `ARGS` environment variable to pass additional arguments
 
 ## Use docker-compose to manage (optional)