[fuzz] Update docs with better OSS-Fuzz link

Change-Id: I1be6bb537139c50342602aacd978585151a4a480
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/443916
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
1 file changed