Pandoc needs to be explicitly installed to build the documentation

[dalonsoa]

While https://pypi.org/project/pandoc/ installs the python wrapper, the underlying library needs to be installed separately. Installation instructions on how to do this should be added to the documentation - only on the developers sections, as end users do not need to build the documentation themselves.

[dalonsoa]

Instructions here: https://pandoc.org/installing.html