Add GitLab badge
<a href="https://github.com/reviewdog/reviewdog/releases">
<img alt="Github All Releases" src="https://img.shields.io/github/downloads/reviewdog/reviewdog/total.svg?maxAge=43200">
</a>
+ <a href="https://gitlab.com/reviewdog/reviewdog/pipelines">
+ <img alt="GitLab Supported" src="https://img.shields.io/badge/GitLab%20-Supported-fc6d26?logo=gitlab">
+ </a>
</p>
<p align="center">
