ci: Remove dependence on travis, use it as fallback env

ci/README.md

@@ -3,6 +3,22 @@
 This directory contains scripts for each build step in each build stage.
 
 Currently three stages `lint`, `extended_lint` and `test` are defined. Each stage has its own lifecycle, similar to the
-[Travis CI lifecycle](https://docs.travis-ci.com/user/job-lifecycle#the-job-lifecycle).  Every script in here is named
+[Travis CI lifecycle](https://docs.travis-ci.com/user/job-lifecycle#the-job-lifecycle). Every script in here is named
 and numbered according to which stage and lifecycle step it belongs to.
 
+### Running a stage locally
+
+To allow for a wide range of tested environments, but also ensure reproducibility to some extent, the test stage
+requires `docker` to be installed. To install all requirements on Ubuntu, run
+
+```
+sudo apt install docker.io ccache bash git
+```
+
+To run the test stage,
+
+```
+./ci/test_run_all.sh
+```
+
+Be aware that the tests will be build and run in-place, so please run at your own risk.