Document release process

Author: AArnott

CONTRIBUTING.md

@@ -41,6 +41,29 @@ Building, testing, and packing this repository can be done by using the standard
 
 [pwsh]: https://docs.microsoft.com/powershell/scripting/install/installing-powershell?view=powershell-6
 
+## Releases
+
+Use `nbgv tag` to create a tag for a particular commit that you mean to release.
+[Learn more about `nbgv` and its `tag` and `prepare-release` commands](https://github.com/dotnet/Nerdbank.GitVersioning/blob/main/doc/nbgv-cli.md).
+
+Push the tag.
+
+### GitHub Actions
+
+When your repo is hosted by GitHub and you are using GitHub Actions, you should create a GitHub Release using the standard GitHub UI.
+Having previously used `nbgv tag` and pushing the tag will help you identify the precise commit and name to use for this release.
+
+After publishing the release, the `.github\workflows\release.yml` workflow will be automatically triggered, which will:
+
+1. Find the most recent `.github\workflows\build.yml` GitHub workflow run of the tagged release.
+1. Upload the `deployables` artifact from that workflow run to your GitHub Release.
+1. If you have `NUGET_API_KEY` defined as a secret variable for your repo or org, any nuget packages in the `deployables` artifact will be pushed to nuget.org.
+
+### Azure Pipelines
+
+When your repo builds with Azure Pipelines, use the `azure-pipelines/release.yml` pipeline.
+Trigger the pipeline by adding the `auto-release` tag on a run of your main `azure-pipelines.yml` pipeline.
+
 ## Tutorial and API documentation
 
 API and hand-written docs are found under the `docfx/` directory. and are built by [docfx](https://dotnet.github.io/docfx/).