Add links to devel in documentation
Would it be useful to add the following links in the standard documentation:
- Future docs: https://yarr.web.cern.ch/yarr/devel/
- Developer docs: https://yarr.web.cern.ch/doxygen/devel/
- Coverage: https://yarr.web.cern.ch/yarr/devel/coverage/
Though some of these are already linked from the README.md file.