Rename to README.testsuite, and bring it up to date.

testsuite/README

-This directory contains automatic test cases for rsync.  You can run
-them yourself if you want, preferably by doing "make check" in the
-top-level source directory.  (Not implemented yet.)
-
-They also run automatically on the build farm, and you can see the
-results on http://build.samba.org/.  That's controlled by the file
-./runlist.

testsuite/README.testsuite

+automatic testsuite for rsync			-*- text -*-
+
+We're trying to develop some more substantial tests to prevent rsync
+regressions.  Ideally, all code changes or bug reports would come with
+an appropriate test suite.
+
+You can run these tests by typing "make check" in the build directory.
+The tests will run using the rsync binary in the build directory, so
+you do not need to do "make install" first.  Indeed, you probably
+should not install rsync before running the tests.
+
+If you instead type "make installcheck" then the suite will test the
+rsync binary found on the path.  You can use this to test a
+distribution build, or perhaps by setting $PATH to run a new test
+suite against an old version of rsync.
+
+If the tests pass, you should see a report to that effect.  Some tests
+require being root or some other precondition, and so will normally be
+checked -- look at the test scripts for more information.
+
+If the tests fail, you will see rather more output.  The scratch
+directory will remain in the build directory.  It would be useful if
+you could include the log messages when reporting a failure.
+
+These tests also run automatically on the build farm, and you can see
+the results on http://build.samba.org/.
+
+