patchtest.README: update name and location or patchtest layer

patchtest.README: update name and location or patchtest layer

The patchtest layer's name and location have changed from:
  patchtest
  https://git.yoctoproject.org/patchtest
to:
  meta-patchtest
  https://git.yoctoproject.org/meta-patchtest

Update any references of the old name and repository to the new ones.

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>