Update Readme

Author: panteparak

README.md

@@ -152,6 +152,10 @@ Finally, start your containers with `VIRTUAL_HOST` environment variables.
 
 [letsencrypt-nginx-proxy-companion](https://github.com/JrCs/docker-letsencrypt-nginx-proxy-companion) is a lightweight companion container for the nginx-proxy. It allow the creation/renewal of Let's Encrypt certificates automatically. 
 
+Set `GENERATE_DHPARAM` environment variable to `false` to disabled Diffie-Hellman parameters completely. This will also ignore auto-generation made by `nginx-proxy`.
+The default value is `true`
+
+     $ docker run -e GENERATE_DHPARAM=false ....
 ### SSL Support
 
 SSL is supported using single host, wildcard and SNI certificates using naming conventions for
@@ -359,4 +363,4 @@ If your system has the `make` command, you can automate those tasks by calling:
     make test
 
 
-You can learn more about how the test suite works and how to write new tests in the [test/README.md](test/README.md) file.
+You can learn more about how the test suite works and how to write new tests in the [test/README.md](test/README.md) file.