diff --git a/README.md b/README.md
index 31460f3..9843ecd 100644
--- a/README.md
+++ b/README.md
@@ -38,7 +38,8 @@ an ACME account), `--acme-file` (`ACME_FILE`; Path to the file where ACME accoun
 are stored in) are additionally required. `--acme-server` (`ACME_SERVER`) should also
 be set to your ACME CA's directory URL as this option defaults to the
 [Let's Encrypt Staging Environment](https://letsencrypt.org/docs/staging-environment/). Note that using this optional implies that you accept your
-configured ACME CA's Terms of Service.
+configured ACME CA's Terms of Service. rio will also spawn an unencrypted HTTP server that is bound to the host specified with `--http-host` (`HTTP_HOST`) and
+the port specified with `--http-port` (`HTTP_PORT`). The functionality of this second HTTP server is to upgrade plain HTTP requests to HTTPS requests.
 
 You can also run with `--debug` (`DEBUG_ENABLE=1`) to enable debug logging.