Including data files in a package

[ChrisOfBristol]

Look at Configuring setup() using setup.cfg files

The above states the following without any explanation of what the elements are:
[options.data_files]
/etc/my_package =
site.d/00_default.conf
host.d/00_default.conf
data = data/img/logo.png, data/svg/icon.svg
fonts = data/fonts/*.ttf, data/fonts/*.otf

I've no idea what site.d... or host.d... mean. I imagine that the line starting data means create a directory called "data" and copy the following files into it. I'll try:
[options.data_files]
data = reference.dat, help.html