Adding a note into About page for making images accessible at Twitter (#476)

* Adding a note into About page for making images accessible at Twitter

* Formatting the page

* update spacing

pages/about.js

@@ -41,10 +41,16 @@ export default () => (
           it a try!
         </p>
         <h4 className="mb0">Export/Sharing</h4>
-        <p className="mt2">
+        <p className="mt2 mb3">
           After you&apos;ve customized your image you can Tweet a link to the image, or save it
           directly.
         </p>
+        <p className="mt2 mb3">
+          If you use the &apos;Tweet&apos; button, Carbon will automatically make your image
+          accessible. However, if you want to manually tweet your carbon image, please check
+          out <a className="link" href="https://help.twitter.com/en/using-twitter/picture-descriptions">this page</a>
+          {' '}to found out how to make your Twitter images accessible.
+        </p>
       </div>
       <div>
         <h2>I want to make this better.</h2>