Add release doc and script:

This doc and helper script is used across other
Tinkerbell repos.

Signed-off-by: Jacob Weinstock <jakobweinstock@gmail.com>

Author: jacobweinstock

RELEASING.md

@@ -0,0 +1,19 @@
+# Releasing
+
+## Process
+
+For version v0.x.y:
+
+1. Create the annotated tag
+   > NOTE: To use your GPG signature when pushing the tag, use `SIGN_TAG=1 ./contrib/tag-release.sh v0.x.y` instead)
+   - `./contrib/tag-release.sh v0.x.y`
+1. Push the tag to the GitHub repository. This will automatically trigger a [Github Action](https://github.com/tinkerbell/hook/actions) to create a release.
+   > NOTE: `origin` should be the name of the remote pointing to `github.com/tinkerbell/boots`
+   - `git push origin v0.x.y`
+1. Review the release on GitHub.
+
+### Permissions
+
+Releasing requires a particular set of permissions.
+
+- Tag push access to the GitHub repository

contrib/tag-release.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+
+set -o errexit -o nounset -o pipefail
+
+if [ -z "${1-}" ]; then
+	echo "Must specify new tag"
+	exit 1
+fi
+
+new_tag=${1-}
+[[ $new_tag =~ ^v[0-9]*\.[0-9]*\.[0-9]*$ ]] || (
+	echo "Tag must be in the form of vX.Y.Z"
+	exit 1
+)
+
+if [[ $(git symbolic-ref HEAD) != refs/heads/main ]] && [[ -z ${ALLOW_NON_MAIN:-} ]]; then
+	echo "Must be on main branch" >&2
+	exit 1
+fi
+if [[ $(git describe --dirty) != $(git describe) ]]; then
+	echo "Repo must be in a clean state" >&2
+	exit 1
+fi
+
+git fetch --all
+
+last_tag=$(git describe --abbrev=0)
+last_tag_commit=$(git rev-list -n1 "$last_tag")
+last_specific_tag=$(git tag --contains="$last_tag_commit" | grep -E "^v[0-9]*\.[0-9]*\.[0-9]*$" | tail -n 1)
+last_specific_tag_commit=$(git rev-list -n1 "$last_specific_tag")
+if [[ $last_specific_tag_commit == $(git rev-list -n1 HEAD) ]]; then
+	echo "No commits since last tag" >&2
+	exit 1
+fi
+
+if [[ -n ${SIGN_TAG-} ]]; then
+	git tag -s -m "${new_tag}" "${new_tag}" &>/dev/null && echo "created signed tag ${new_tag}" >&2 && exit
+else
+	git tag -a -m "${new_tag}" "${new_tag}" &>/dev/null && echo "created annotated tag ${new_tag}" >&2 && exit
+fi