Update class-bjgk-genesis-enews-extended.php

Add file-level DocBlock.

Not changed in this commit, but the `@link` should point somewhere more specific for this plugin - either the .org repo, this GitHub repo, or a page on BK.com specifically for the plugin (if it exists).
Merge pull request #28 from GaryJones/patch-1

Update class-bjgk-genesis-enews-extended.php to include file-level DocBlock