docs(emoji): Change emoji comment (#611)

Fix emoji comment to reflect its actual behavior

src/subParsers/makehtml/emoji.js

@@ -1,6 +1,7 @@
 /**
- * These are all the transformations that occur *within* block-level
- * tags like paragraphs, headers, and list items.
+ * Turn emoji codes into emojis
+ *
+ * List of supported emojis: https://github.com/showdownjs/showdown/wiki/Emojis
  */
 showdown.subParser('makehtml.emoji', function (text, options, globals) {
   'use strict';