kselftest: Move the docs to the Documentation dir

Also, adjust the formatting a bit, and expand the section about using
TARGETS= on the make command line.

Signed-off-by: Tim Bird <tim.bird@sonymobile.com>
Acked-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

tools/testing/selftests/README.txt

@@ -1,61 +0,0 @@
-Linux Kernel Selftests
-
-The kernel contains a set of "self tests" under the tools/testing/selftests/
-directory. These are intended to be small unit tests to exercise individual
-code paths in the kernel.
-
-On some systems, hot-plug tests could hang forever waiting for cpu and
-memory to be ready to be offlined. A special hot-plug target is created
-to run full range of hot-plug tests. In default mode, hot-plug tests run
-in safe mode with a limited scope. In limited mode, cpu-hotplug test is
-run on a single cpu as opposed to all hotplug capable cpus, and memory
-hotplug test is run on 2% of hotplug capable memory instead of 10%.
-
-Running the selftests (hotplug tests are run in limited mode)
-=============================================================
-
-To build the tests:
-
-  $ make -C tools/testing/selftests
-
-
-To run the tests:
-
-  $ make -C tools/testing/selftests run_tests
-
-- note that some tests will require root privileges.
-
-To run only tests targeted for a single subsystem: (including
-hotplug targets in limited mode)
-
-  $  make -C tools/testing/selftests TARGETS=cpu-hotplug run_tests
-
-See the top-level tools/testing/selftests/Makefile for the list of all possible
-targets.
-
-Running the full range hotplug selftests
-========================================
-
-To build the tests:
-
-  $ make -C tools/testing/selftests hotplug
-
-To run the tests:
-
-  $ make -C tools/testing/selftests run_hotplug
-
-- note that some tests will require root privileges.
-
-Contributing new tests
-======================
-
-In general, the rules for for selftests are
-
- * Do as much as you can if you're not root;
-
- * Don't take too long;
-
- * Don't break the build on any architecture, and
-
- * Don't cause the top-level "make run_tests" to fail if your feature is
-   unconfigured.