Pass path to command dynamically in Dockerfile

README.md

@@ -43,11 +43,11 @@
 
 ### build site
 
-    $ docker run --rm -w /opt -v $PWD:/opt sitegen-openresty sitegen
+    $ docker run --rm -w /opt/app -v $PWD:/opt/app sitegen-openresty sitegen
 
-### start server container
+### start server
 
-    $ docker run --rm -it --init -w /opt -v $PWD:/opt -p 8080:8080 sitegen-openresty
+    $ docker run --rm -it --init -v $PWD:/opt/app -p 8080:8080 sitegen-openresty
 
 ### visit `localhost:8080` in web browser