1. Started by cloning RTD template: https://docs.readthedocs.io/en/stable/tutorial/ into github repository;
2. Clone github repository to local directory;
3. In the local copy: adapt conf.py (changed project name, author, ...);
4. In the local copy: Remove lumache.py;
5. In the local copy: create folder src, containing test source code;
6. In the local copy: copy documentation (generated using exhale, breathe, doxygen and sphinx) into docs/source; - replaced index.rst and created/copied folder api;
7. Add, commit, push;
8. Deploy to RTD;

Result: The file hierarchy is accessed in https://mylvglwatch.readthedocs.io/en/latest/api/library_root.html# but the documentation embedded as comments in the source-code is not shown.

1. Change conf.py to run breathe;
2. add folder _doxygen and its contents;

Result: RTD compilation failed. It did not find breathe. Googled to a solution. Found: breathe-doc/breathe#89 and https://github.com/Cruel/readthedocs-breathe/tree/master/docs. Noticed that I missed file requirements.txt. Included it to my repo. It compiled and the source-code embedded documentation appeared.