added release from a branch

Signed-off-by: Patrick Zheng <patrickzheng@microsoft.com>

RELEASE_CHECKLIST.md

@@ -4,14 +4,27 @@
 
 This document describes the checklist to publish a release for notation-go.
 
-## Release Process
+## Release Process from main
 
 1. Check if there are any security vulnerabilities fixed and security advisories published before a release. Security advisories should be linked on the release notes.
-2. Determine a [SemVer2](https://semver.org/)-valid version prefixed with the letter `v` for release. For example, `v1.0.0-rc.1`.
+2. Determine a [SemVer2](https://semver.org/)-valid version prefixed with the letter `v` for release. For example, `version="v1.0.0-rc.1"`.
 3. If there is new release in [notation-core-go](https://github.com/notaryproject/notation-core-go) library that are required to be upgraded in notation-go, update the dependency versions in the follow `go.mod` and `go.sum` files of notation-go:
     - [go.mod](go.mod), [go.sum](go.sum)
-4. Update the value of `signingAgent` defined in file `signer/signer.go` with `notation-go/<version>`, where `<version>` is the SemVer2 value from step 2 without the `v` prefix. For example, `notation-go/1.0.0-rc.1`.
+4. Update the value of `signingAgent` defined in file `signer/signer.go` with `notation-go/<version>`, where `<version>` is `$version` from step 2 without the `v` prefix. For example, `notation-go/1.0.0-rc.1`.
 5. Open a bump up PR and submit the changes in step 3 and 4 to the notation-go repository.
-6. After PR from step 5 is merged. Create a vote issue for the new release cut at the PR's commit hash. Add the link of change logs and repo-level maintainer list in the issue's description. The issue title should be `vote: tag <version>`. A majority of approvals from the [repo-level maintainers](MAINTAINERS) MUST be met before releasing. An example vote [issue](https://github.com/notaryproject/notation-go/issues/341).
-7. On notation-go GitHub page, click [Releases](https://github.com/notaryproject/notation-go/releases) and then click `Draft a new release`. In the draft a new release page, create the tag with name `<version>`. Then click `Generate release notes`. Check the draft release, revise the release description, and publish the release. Close the vote issue once accomplished.
-8. Announce the new release in the Notary Project community.
+6. After PR from step 5 is merged. Create a vote issue for the new release cut at the PR's commit hash. Add the link of change logs and repo-level maintainer list in the issue's description. The issue title should be `vote: tag $version`. A majority of approvals from the [repo-level maintainers](MAINTAINERS) MUST be met before releasing. An example vote [issue](https://github.com/notaryproject/notation-go/issues/341).
+7. On notation-go GitHub page, click [Releases](https://github.com/notaryproject/notation-go/releases) and then click `Draft a new release`. In the draft a new release page, create the tag with name `$version`. Then click `Generate release notes`. Check the draft release, revise the release description, and publish the release. Close the vote issue once accomplished.
+8. Announce the new release in the Notary Project community.
+
+## Release Process from a release branch
+
+1. Check if there are any security vulnerabilities fixed and security advisories published before a release. Security advisories should be linked on the release notes.
+2. Determine a [SemVer2](https://semver.org/)-valid version prefixed with the letter `v` for release. For example, `version="v1.2.0-rc.1"`.
+3. If a new release branch is needed, from main branch [commit list](https://github.com/notaryproject/notation-go/commits/main/), find the commit that you want to cut the release. Click `<>` (Browse repository at this point). Create branch with name `release-<version>` from the commit, where `<version>` is `$version` from step 2 with the major and minor versions only. For example `release-1.2`. If the release branch already exists, skip this step.
+4. If there is new release in [notation-core-go](https://github.com/notaryproject/notation-core-go) library that are required to be upgraded in notation-go, update the dependency versions in the follow `go.mod` and `go.sum` files of notation-go:
+    - [go.mod](go.mod), [go.sum](go.sum)
+5. Update the value of `signingAgent` defined in file `signer/signer.go` with `notation-go/<version>`, where `<version>` is `$version` from step 2 without the `v` prefix. For example, `notation-go/1.2.0-rc.1`.
+6. Open a bump up PR and submit the changes in step 4 and 5 to the release branch. The PR also needs to include any commit from main branch that you would like to include in the release (you can do this by `git cherry-pick` command). 
+7. After PR from step 6 is merged. Create a vote issue for the new release cut at the PR's commit hash. Add the link of change logs and repo-level maintainer list in the issue's description. The issue title should be `vote: tag $version`. A majority of approvals from the [repo-level maintainers](MAINTAINERS) MUST be met before releasing. An example vote [issue](https://github.com/notaryproject/notation-go/issues/439).
+8. On notation-go GitHub page, click [Releases](https://github.com/notaryproject/notation-go/releases) and then click `Draft a new release`. In the draft a new release page, create the tag with name `$version`. Set the `Target` branch as `release-<version>` as in step 3. Then click `Generate release notes`. Check the draft release, revise the release description, and publish the release. Close the vote issue once accomplished.
+9. Announce the new release in the Notary Project community.