Bug 25691: Replace link to non-existing README with wiki link

Bug 25691: Replace link to non-existing README with wiki link

This doesn't update the occurrence in the control file
as it says in control.in:

To test:
* Verify all occurrences of the README file have been updated. Exceptions:
  * control (see above)
  * changelog

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit 0a49f71e8f0bad53dbdfd48bfc2beddbff89a6cc)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>