adding core doxygen links to the doc

[PhilLAL]

Hi,
it seems https://tango-controls.github.io/cppTango-docs/ is not mentioned into the doc, it seems useful to add them somewhere into the doc. Probably similar core docs should be added doc python and java.

Do you see a reason why not add it?
If you agree, where do you think it should be added?

[bourtemb]

It is already there: https://tango-controls.readthedocs.io/en/latest/development/cpp-api/index.html

But it might be interesting to highlight it a bit more? Suggestions?

[PhilLAL]

My fault, I only does a research by keyword in tango readthedocs on "https://tango-controls.github.io/cppTango-docs/" did not give me any result, and "cppTango-docs" returns me https://tango-controls.readthedocs.io/en/latest/search.html?q=%22cppTango-docs%22&check_keywords=yes&area=default#
I'm not sure a highlight is needed.