Example project that shows how to use GNAT Community 2018 in Travis CI.
Enable Travis-CI on your repository. This can be done by going to your settings on travis-ci.com.
Copy the .travis.yml file and the contents of the scripts folder to your repository. You need to adapt the end of the .travis.yml to your project. Pushing these files via a new commit to a repository should trigger a build, which you can see on the travis interface.
Add the badge to your project. In the Travis-CI interface, click on the build status logo. It will open a dialogue where you can select Markdown syntax, that you can then copy-paste to your README.md.