feat: add ability to create pre-release tags (#17)

Reviewed-on: #17
Co-authored-by: Timo Behrendt <t.behrendt@t00n.de>
Co-committed-by: Timo Behrendt <t.behrendt@t00n.de>

README.md

@@ -43,6 +43,15 @@ jobs:
     token: ${{ secrets.GITHUB_TOKEN }}
 ```
 
+### With prerelease tags
+
+```yaml
+- uses: tbehrendt/conventional-semantic-git-tag-increment@v1
+  with:
+    prerelease: "true"
+    token: ${{ secrets.GITHUB_TOKEN }}
+```
+
 ## Examples
 
 | Commit Message                      | Current Tag | New Tag  | Reason               |
@@ -52,11 +61,20 @@ jobs:
 | `feat!: change API response format` | `v1.1.1`    | `v2.0.0` | Breaking change      |
 | `docs: update README`               | `v2.0.0`    | `v2.0.1` | Documentation update |
 
+### Prerelease Examples
+
+| Commit Message                  | Current Tag | New Tag (prerelease) | Reason      |
+| ------------------------------- | ----------- | -------------------- | ----------- |
+| `feat: add user authentication` | `v1.0.0`    | `1.1.0-rc-abc123`    | New feature |
+| `fix: resolve login bug`        | `v1.1.0`    | `1.1.1-rc-def456`    | Bug fix     |
+
 ## Inputs
 
 - `last-tag` (optional): Starting tag to increment from. If not provided, uses the latest tag in the repository.
 - `token` (required): GitHub token for repository access. Use `${{ github.token }}` for public repos or a PAT for private repos.
+- `prerelease` (optional): Whether to create a prerelease tag with `-rc-<github.sha>` suffix. Defaults to `false`.
+- `max-tags` (optional): Maximum number of tags to fetch when looking for the latest non-pre-release tag. Defaults to `50`.
 
 ## Outputs
 
-- `new-tag`: The incremented semantic version tag (e.g., `1.2.3`)
+- `new-tag`: The incremented semantic version tag (e.g., `1.2.3` or `1.2.3-rc-abc123` for prerelease)