qnx4: credit contributors in CREDITS

Replace the content of the qnx4 README file with the canonical place for
such information.

Add the credits of the qnx4 contribution to CREDITS. As there is already a
QNX4 FILESYSTEM section in MAINTAINERS, it is clear who to contact and send
patches to.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-By: Anders Larsen <al@alarsen.net>
Link: https://lore.kernel.org/r/20230220170210.15677-3-lukas.bulwahn@gmail.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>