feat: add input to enable gpg commit signing

README.md

@@ -50,6 +50,7 @@ All inputs are **optional**. If not set, sensible defaults will be used.
 | `committer` | The committer name and email address in the format `Display Name <[email protected]>`. Defaults to the GitHub Actions bot user. | `GitHub <[email protected]>` |
 | `author` | The author name and email address in the format `Display Name <[email protected]>`. Defaults to the user who triggered the workflow run. | `${{ github.actor }} <${{ github.actor }}@users.noreply.github.com>` |
 | `signoff` | Add [`Signed-off-by`](https://git-scm.com/docs/git-commit#Documentation/git-commit.txt---signoff) line by the committer at the end of the commit log message. | `false` |
+| `gpg-sign` | GPG-sign commits. See [GPG commit signature verification](docs/concepts-guidelines.md#gpg-commit-signature-verification) for details. | `false` |
 | `branch` | The pull request branch name. | `create-pull-request/patch` |
 | `delete-branch` | Delete the `branch` when closing pull requests, and when undeleted after merging. Recommend `true`. | `false` |
 | `branch-suffix` | The branch suffix type when using the alternative branching strategy. Valid values are `random`, `timestamp` and `short-commit-hash`. See [Alternative strategy](#alternative-strategy---always-create-a-new-pull-request-branch) for details. | |