Update README.md

Author: bigabig

README.md

@@ -66,7 +66,7 @@ git clone https://github.com/uhh-lt/dats.git
 #### 2. Run setup scripts
 
 ```bash
-./bin/setup-envs.sh --project_name dats --port-prefix 101
+./bin/setup-envs.sh --project_name dats --port_prefix 101
 ```
 
 ```bash