Update README.md

README.md

@@ -13,6 +13,14 @@ These _glyphsets_ are not to be confused with the _subsets_ that the [Google Fon
 
 These subsets used to be hosted here in this repository, but are not found over in the newly created [nam-files](https://github.com/googlefonts/nam-files) repo. 
 
+What’s the difference?
+----------------------
+
+As a user of the Google Fonts API you may request a multi-script font to be served limited to a _subset_, usually a certain script, such as `https://fonts.googleapis.com/css?family=Roboto+Mono&subset=cyrillic`, to speed up file transfer by leaving out unnecessary glyphs.
+
+_Glyphsets_ on the other hand are what Google Fonts requires font authors to put into fonts when designing them, and they’re not identical to subsets. You can get a font’s complete glyphset by manually downloading a TTF on [fonts.google.com](https://fonts.google.com/), but you typically don’t get the same glyphs in a font accessed through the Google Fonts API because these are subsetted.
+
+
 Glyphsets for font authoring
 ----------------------------