Document how to run SPLAT

Signed-off-by: Brian Behlendorf <[email protected]>
Closes openzfs#294

README.markdown

@@ -22,5 +22,13 @@ compilation:
     $ ./configure --enable-linux-builtin --with-linux=/usr/src/linux-...
     $ ./copy-builtin /usr/src/linux-...
 
-Full documentation for building, configuring, and using the SPL can
-be found at: <http://zfsonlinux.org>
+The SPL comes with an automated test suite called SPLAT.  The test suite
+is implemented in two parts.  There is a kernel module which contains
+the tests and a user space utility which controls which tests are run.
+To run the full test suite:
+
+    $ sudo insmod ./module/splat/splat.ko
+    $ sudo ./cmd/splat --all
+
+Full documentation for building, configuring, testing, and using the
+SPL can be found at: <http://zfsonlinux.org>