Documentation/dev-tools: Add kselftest

Move kselftest.txt to dev-tools/kselftest.rst .
Signed-off-by: NMickaël Salaün <mic@digikod.net>
Acked-by: NKees Cook <keescook@chromium.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>

Documentation/00-INDEX

@@ -246,8 +246,6 @@ kprobes.txt
 	- documents the kernel probes debugging feature.
 kref.txt
 	- docs on adding reference counters (krefs) to kernel objects.
-kselftest.txt
-	- small unittests for (some) individual codepaths in the kernel.
 laptops/
 	- directory with laptop related info and laptop driver documentation.
 ldm.txt