Fixed Docker run command

README.md

@@ -15,10 +15,10 @@ Configure desktop by export DESKTOP variable. May be a river or sway.
 
 Run the build for Sway:
 
-    export DESKTOP=sway
     docker run --privileged -i -v /proc:/proc \
         -v ${PWD}:/working_dir \
         -w /working_dir \
+        -e DESKTOP=sway \
         debian:latest \
         /bin/bash -s etc/terraform.conf < build.sh