Add release guide to CONTRIBUTING.md

Author: johanbrandhorst

CONTRIBUTING.md

@@ -4,14 +4,14 @@ Thank you for your contribution to grpc-gateway.
 Here's the recommended process of contribution.
 
 1. `go get github.com/grpc-ecosystem/grpc-gateway/protoc-gen-grpc-gateway`
-2. `cd $GOPATH/src/github.com/grpc-ecosystem/grpc-gateway`
-3. hack, hack, hack...
-4. Make sure that your change follows best practices in Go
+1. `cd $GOPATH/src/github.com/grpc-ecosystem/grpc-gateway`
+1. hack, hack, hack...
+1. Make sure that your change follows best practices in Go
    - [Effective Go](https://golang.org/doc/effective_go.html)
    - [Go Code Review Comments](https://golang.org/wiki/CodeReviewComments)
-5. Make sure that `go test ./...` passes.
-6. Sign [a Contributor License Agreement](https://cla.developers.google.com/clas)
-7. Open a pull request in Github
+1. Make sure that `go test ./...` passes.
+1. Sign [a Contributor License Agreement](https://cla.developers.google.com/clas)
+1. Open a pull request in Github
 
 When you work on a larger contribution, it is also recommended that you get in touch
 with us through the issue tracker.
@@ -36,3 +36,22 @@ docker run -itv $(pwd):/grpc-gateway -w /grpc-gateway --entrypoint /bin/bash --r
 ```
 
 If this has resulted in some file changes in the repo, please ensure you check those in with your merge request.
+
+### Making a release
+
+To make a release, follow these steps:
+
+1. Decide on a release version. The `gorelease` job can
+    recommend whether the new release should be a patch or minor release.
+    See [CircleCI](https://app.circleci.com/pipelines/github/grpc-ecosystem/grpc-gateway/126/workflows/255a8a04-de9c-46a9-a66b-f107d2b39439/jobs/6428)
+    for an example.
+1. Generate a Github token with `repo` access.
+1. Create a new branch and edit the Makefile `changelog` job, settings
+    the `future-release=` variable to the name of the version you plan to release
+1. Run `CHANGELOG_GITHUB_TOKEN=<yourtoken> make changelog`
+1. Commit the `Makefile` and `CHANGELOG.md` changes.
+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. (Optional) Delete your Github token again.
+1. (Required) Sit back and pat yourself on the back for a job well done :clap:.