Add a design note, hopefully addressing #10 👍

Author: developit

README.md

@@ -15,6 +15,8 @@
 - **Functional:** methods don't rely on `this`
 - **Great Name:** somehow [mitt](https://npm.im/mitt) wasn't taken
 
+> Mitt was made for the browser, but works in any JavaScript runtime. It has no dependencies and only uses basic language features. It probably works in Internet Explorer 5.
+
 
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