Create release documentation (#373)

Signed-off-by: Hayden B <[email protected]>

Author: haydentherapper

RELEASE.md

@@ -0,0 +1,42 @@
+# Releasing rekor-tiles
+
+## Publishing updated binary and container
+
+This guide assumes that `upstream` references github.com/sigstore/rekor-tiles.
+
+Create and push a new tag. Note that you can't create a tag without creating a release in the GitHub UI, so you'll need to do this locally.
+
+```
+git pull upstream main
+export RELEASE_TAG=v1.2.3 # Specify version
+git tag -s ${RELEASE_TAG} -m "${RELEASE_TAG}"
+git push upstream ${RELEASE_TAG}
+```
+
+After the tag is pushed, two workflows will kick off:
+
+* [Create release](https://github.com/sigstore/rekor-tiles/actions/workflows/release.yml)
+* [Create and publish Docker image](https://github.com/sigstore/rekor-tiles/actions/workflows/build_container.yml)
+
+Once "Create release" finishes, go to [Releases](https://github.com/sigstore/rekor-tiles/releases), select
+the latest draft release, and publish it. If the release is pre-1.0, select "Set as a pre-release" before publishing.
+
+## Updating the infrastructure
+
+Update the [Helm chart](https://github.com/sigstore/helm-charts/tree/main/charts/rekor-tiles) to the latest version.
+Follow [this example](https://github.com/sigstore/helm-charts/pull/989/).
+
+Get the container digest:
+
+```
+crane digest ghcr.io/sigstore/rekor-tiles:v1.2.3 # Specify version
+```
+
+Update `charts/rekor-tiles/values.yaml` with the new container version and digest.
+
+Update `charts/rekor-tiles/Chart.yaml`, bumping `version`, `appVersion`, and the image reference.
+
+Run `helm-docs -g charts/rekor-tiles` to update the README.
+
+Create a PR and wait for an oncall engineer to approve and merge. An oncall engineer also needs to
+update the chart version on the PGI repo.