Update weblinks
Fix readme links to point to correct website (former ~/nifty/nifty8/ is now the default page ~/nifty/)
The old module-image for the shared runners will be discontinued on October 31. All users still referencing gitlab-registry.mpcdf.mpg.de/mpcdf/module-image in their CI pipelines need to switch to the new CI images now, see instructions here.
Fix readme links to point to correct website (former ~/nifty/nifty8/ is now the default page ~/nifty/)