[doxygen] How to make an introduction page with Doxygen

I tried all the above with v 1.8.13 to no avail. What worked for me (on macOS) was to use the doxywizard->Expert tag to fill the USE_MD_FILE_AS_MAINPAGE setting.

It made the following changes to my Doxyfile:

USE_MDFILE_AS_MAINPAGE = ../README.md
...
INPUT                  = ../README.md \
                         ../sdk/include \
                         ../sdk/src

Note the line termination for INPUT, I had just been using space as a separator as specified in the documentation. AFAICT this is the only change between the not-working and working version of the Doxyfile.