Merge pull request #3 from Yoast/stories/af/clarify-polite-assertive-…

…usage

Clarify usage of polite and assertive messages.

README.md

@@ -25,5 +25,9 @@ To make the `wp.a11y.speak` functionality more universally available, we've deci
 ```JS
 var A11ySpeak = require("A11ySpeak");
 
-A11ySpeak( "The message you want to send to the ARIA live region", "polite" );
+// For polite messages that shouldn't interrupt what screen readers are currently announcing.
+AllySpeak( "The message you want to send to the ARIA live region" );
+
+// For assertive messages that should interrupt what screen readers are currently announcing.
+AllySpeak( "The message you want to send to the ARIA live region", "assertive" );
 ```