[doc] Add github action status badge to the main readme
</h1>
<p align="center">
+ <a href="https://github.com/Ericsson/codechecker/actions">
+ <img src="https://github.com/Ericsson/codechecker/workflows/codechecker-tests/badge.svg"
+ alt="Github Action">
+ </a>
<a href="https://gitter.im/codecheckerHQ/Lobby?utm_source=share-link&utm_medium=link&utm_campaign=share-link">
<img src="https://badges.gitter.im/codecheckerHQ/Lobby.svg"
alt="Gitter">
