selftests: add a simple doc
selftests: add a simple doc

This change adds a little documentation to the tests under
tools/testing/selftests/, based on akpm's explanation.

[5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org: move from Documentation to tools/testing/selftests/README.txt]
Signed-off-by: Jeremy Kerr <68a658b44bbaefab3ef5cd231967195fc0ff9d69@ozlabs.org>
Cc: Dave Young <5716cc40769303914dac486db0fc6ac4cba9419e@redhat.com>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs