Update README.md

Author: J. Ky Marsh

README.md

@@ -68,6 +68,14 @@ them with the community!
 Check out the [nuclide-molecules](https://github.com/jkymarsh/nuclide-molecules) repo for
 sample Molecules.
 
+### Browser support
+
+All styles generated by nuclide, as well as all official nuclide Molecules, support down
+to IE8.
+
+Keep in mind that nuclide is mobile-first, so users on IE8 will, by default, see mobile
+styles!
+
 ### Caveats
 
 - nuclide doesn't include a normalize, reset, grid, etc. Don't forget to include your favorites!