test: Document how to run the test suite

Signed-off-by: Jacques de Laval <jacques@de-laval.se>

test/README.md

@@ -0,0 +1,26 @@
+Tests
+=====
+
+Finit comes with a set of tests and a small framework for running them.
+Contributors are encouraged to write new tests when implementing features, or
+fixing bugs.
+
+Each test is run in isolation, in it's own namespace. Finit will therefore
+be able to be launched as PID 1. Since it's also running with it's own root
+directory it will be able to function properly without having any super user
+privileges in the host environment.
+
+Running tests
+-------------
+
+To run the test suite, first [build](../doc/build.md) Finit - then simply run:
+
+    make check
+
+`make check` will set up the required assets for the test environment, and then
+run the full set of tests. The environment is not removed afterwards so at
+this point individual tests can be executed without having to run the entire
+test suite, which is handy when developing new tests or debugging existing
+test. To execute an individual test, simply invoke the script containing it:
+
+    ./test/name-of-the-test.sh