Add comment noting a dependency on fontconfig data files in fonts.conf.
Add comment noting a dependency on fontconfig data files in fonts.conf.

This had stopped working for me when I locally updated fontconfig but
did not update the data files.

dougfelt/nototools,googlefonts/nototools,googlei18n/nototools,googlefonts/nototools,googlei18n/nototools,moyogo/nototools,googlefonts/nototools,googlefonts/nototools,googlefonts/nototools,anthrotype/nototools,dougfelt/nototools,moyogo/nototools,moyogo/nototools,dougfelt/nototools,anthrotype/nototools,googlei18n/nototools,anthrotype/nototools