Add more instructions on the GitHub releases UI

CONTRIBUTING.md

@@ -58,5 +58,9 @@ To make a release, follow these steps:
 1. Open a PR and check that everything looks right.
 1. Merge the PR.
 1. Tag the release on `master`, the tag should be made against the commit you just merged.
+   1. The release can be created using the command line, or also through GitHub's [releases
+      UI](https://github.com/grpc-ecosystem/grpc-gateway/releases/new).
+   1. If you create a release using the web UI you can publish it as a draft and have it
+      reviewed by another maintainer.
 1. (Optional) Delete your Github token again.
 1. (Required) Sit back and pat yourself on the back for a job well done :clap:.