Update README.md

Added basic description and install how-to.

README.md

@@ -1,2 +1,15 @@
-# qlplayground
-Quick Look support for Swift Playgrounds
+QLPlayground
+================================
+**QLPlayground** is a QuickLook generator for Xcode Playgrounds. Supports both single and multiple paged playgrounds.
+
+Installation
+------------
+
+To install, build the `QLPlayground` target and move the `QLPlayground.qlgenerator` into `~/Library/QuickLook/` or into `/Library/QuickLook/`. Later will make it available for all users.
+Optionally run `qlmanage -r` to reload QL generators.
+
+Customization
+-------------
+
+The generator uses [SyntaxHighlighter](http://alexgorbatchev.com/SyntaxHighlighter/) to highlight the source. You can customize the output by editing files under `.../QLPlayground.qlgenerator/Contents/Resources/`. 
+