Update README.rst

Saving someone the hour I just wasted before stumbling upon this issue.

README.rst

@@ -23,4 +23,8 @@ the new Powerline plugin.
 patched font! See the `Powerline font installation instructions`__ for
 details.
 
-__ https://powerline.readthedocs.org/en/latest/installation/linux.html#font-installation
+__ https://powerline.readthedocs.org/en/latest/installation/linux.html#font-installation
+
+iTerm2 users need to set both the Regular font and the Non-ASCII Font in "iTerm > Preferences > Text" to use a patched font (per `this issue`__).
+
+__ https://github.com/Lokaltog/powerline-fonts/issues/44