Add a note on fonts.

README.md

@@ -41,6 +41,16 @@ spaces followed by an asterisk `*`.
 the value ` /twiki/pub`, which happens to be the prefix of the CSS file’s 
 upload path.
 
+### Fonts
+
+Right now, the stylesheet assumes you have ‘Source’ family of fonts from Adobe 
+installed. These are good-looking, freely available, open source fonts 
+available to download on Github:
+
+* [Source Serif Pro][source-serif]
+* [Source Sans Pro][source-sans]
+* [Source Code Pro][source-code]
+
 JavaScript Installation instructions
 ------------------------------------
 
@@ -68,3 +78,6 @@ outrageously offensive, but it could be better.
 
 [katex]: https://khan.github.io/KaTeX/
 [tampermonkey]: http://tampermonkey.net
+[source-serif]: https://github.com/adobe-fonts/source-serif-pro
+[source-sans]: https://github.com/adobe-fonts/source-sans-pro
+[source-code]: https://github.com/adobe-fonts/source-code-pro