Dalston: Update theme description to match showcase.

dalston/sass/style-child-theme.scss

@@ -3,7 +3,7 @@ Theme Name: Dalston
 Theme URI: https://github.com/Automattic/themes/dalston
 Author: Automattic
 Author URI: https://automattic.com/
-Description: A design system for WordPress sites built with Gutenberg.
+Description: Make your online portfolio impressively awesome with Dalston. With the ability to beautifully highlight your illustration and other projects, Dalston is also versatile enough to be your personal site too.
 Requires at least: WordPress 4.9.6
 Version: 1.0.0
 License: GNU General Public License v2 or later

dalston/style-rtl.css

@@ -4,7 +4,7 @@ Theme Name: Dalston
 Theme URI: https://github.com/Automattic/themes/dalston
 Author: Automattic
 Author URI: https://automattic.com/
-Description: A design system for WordPress sites built with Gutenberg.
+Description: Make your online portfolio impressively awesome with Dalston. With the ability to beautifully highlight your illustration and other projects, Dalston is also versatile enough to be your personal site too.
 Requires at least: WordPress 4.9.6
 Version: 1.0.0
 License: GNU General Public License v2 or later

dalston/style.css

@@ -4,7 +4,7 @@ Theme Name: Dalston
 Theme URI: https://github.com/Automattic/themes/dalston
 Author: Automattic
 Author URI: https://automattic.com/
-Description: A design system for WordPress sites built with Gutenberg.
+Description: Make your online portfolio impressively awesome with Dalston. With the ability to beautifully highlight your illustration and other projects, Dalston is also versatile enough to be your personal site too.
 Requires at least: WordPress 4.9.6
 Version: 1.0.0
 License: GNU General Public License v2 or later