DOC: note in readme regarding tests

README.md

@@ -9,3 +9,10 @@ This project contains the "base" of an FSL installation. It includes:
 Prior to FSL 6.0.X, the contents of this project were provided by the
 [etc](https://git.fmrib.ox.ac.uk/fsl/etc) and
 [config](https://git.fmrib.ox.ac.uk/fsl/config) projects.
+
+
+## Tests
+
+The `.ci` directory contains a collection of tests which validate the
+behaviour of various aspects of the `base` project. All tests are written
+in Python, and are executed with `pytest`.