add readme

+This is to test the several implementations of Debian version comparison
+algorithms.
+
+Run it via `make test`.
+
+`run.py` generates a file containing all permutations of pairs of versions. The
+different programs then check whether versions are greater than, equal or less
+than one another and output >, = and <, respectively in order. It is then
+checked whether the output of all implementations is the same.