docs: update readme

README.md

@@ -66,10 +66,12 @@ $ curl -L https://wakapi.dev/get | bash
 # Create a persistent volume
 $ docker volume create wakapi-data
 
+$ SALT="$(cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w ${1:-32} | head -n 1)"
+
 # Run the container
 $ docker run -d \
   -p 3000:3000 \
-  -e "WAKAPI_PASSWORD_SALT=$(cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w ${1:-32} | head -n 1)" \
+  -e "WAKAPI_PASSWORD_SALT=$SALT" \
   -v wakapi-data:/data \
   --name wakapi \
   ghcr.io/muety/wakapi:latest