Add assets (#6)

* Add `assets` folder. Update `readme.txt`

* Add icons

* Add banners

README.md

@@ -1,8 +1,12 @@
 # wp-quip
 
+![WP Quip plugin Settings page](assets/icon-128×128.png)
+
+
 [Quip](https://quip.com/) integration for WordPress
 
 
+
 ## Introduction
 
 `WP Quip` plugin uses WordPress shortcodes to embed [Quip](https://quip.com/) documents into WordPress pages and blog posts.
@@ -30,7 +34,7 @@ https://codex.wordpress.org/Shortcode_API
 #
 #### WP Quip plugin Settings page
 
-![WP Quip plugin Settings page](screenshot-1.png)
+![WP Quip plugin Settings page](assets/screenshot-1.png)
 
 
 
@@ -66,13 +70,19 @@ and then set `ttl` back to its original value.
 #
 #### WordPress post editor with a `quip` shortcode
 
-![WordPress post editor with a 'quip' shortcode](screenshot-2.png)
+![WordPress post editor with a 'quip' shortcode](assets/screenshot-2.png)
+
+
+#
+#### Quip document embedded into a WordPress blog post
+
+![Quip document embedded into a WordPress blog post](assets/screenshot-3.png)
 
 
 #
 #### Quip document embedded into a WordPress blog post
 
-![Quip document embedded into a WordPress blog post](screenshot-3.png)
+![Quip document embedded into a WordPress blog post](assets/screenshot-4.png)
 
 
 ## References

readme.txt

@@ -1,7 +1,7 @@
 === WP Quip ===
 Contributors:
 Tags: quip, doc
-Donate link: https://cloudposse.com/
+Donate link:
 Requires at least: 4.0
 Tested up to: 4.9.2
 Requires PHP: 5.6
@@ -66,12 +66,19 @@ NOTE: To generate a Quip API Access Token, visit this page: https://quip.com/dev
 Whenever you generate a new token, all previous tokens are automatically invalidated.
 
 
+== Frequently Asked Questions ==
+
+
 == Screenshots ==
 1. WP Quip plugin Settings page
 2. WordPress post editor with a 'quip' shortcode
 3. Quip document embedded into a WordPress blog post
+4. Quip document embedded into a WordPress blog post
 
 
 == Changelog ==
 = 1.0 =
 * Initial release.
+
+
+== Upgrade Notice ==