add content to about faq page

This reads like som kind of abstract, probably going to expand a little
bit.

Author: mseeber

faq/about.md

@@ -4,4 +4,7 @@ title: "About Jack"
 ---
 
 JACK (JACK Audio Connection Kit) refers to an [API](/api) and two
-implementations of this API, jack1 and jack2.
+implementations of this API, jack1 and jack2. It provides a basic
+infrastructure for audio applications to communicate with each other and
+with audio hardware.  Through JACK, users are enabled to build powerful
+systems for signal processing and music production.