README.qmd does not render in a correct format for github

[wolass]

Describe the bug
After rendering README.qmd we are expecting to get a README.md file that will be nicely presented on the github page.
Currently the use of output: github_document in the yaml heading is no more recognized by a new version of quarto.

Therefore according to this documentation we should be using format: gfm.

To Reproduce

just make a new compendium using rrtools::create_compendium() and render README.qmd.

This results in rendering a README.html and not README.md.

Expected behavior
Rendering README.qmd should produce README.md that is recognized by github.