Add build and download instructions to Readme

Author: thecatalinstan

Readme.md

@@ -13,12 +13,27 @@ Funky maintains a list of apps for which it will set the function key to standar
 
 Use GitHub's [issue tracker](https://github.com/thecatalinstan/Funky/issues) to submit bug reports feature requests, or just to say hi.
 
-## Privacy Policy
+## Pre-Built Binaries
 
-Please carefully read the [Privacy Policy](https://github.com/thecatalinstan/Funky/blob/master/Privacy.md).
+You can download pre-built binaries of Funky from two sources:
+
+- **GitHub:** see the [Releases](https://github.com/thecatalinstan/Funky/releases) section. [https://github.com/thecatalinstan/Funky/releases](https://github.com/thecatalinstan/Funky/releases)
+- **Mac AppStore:** free to download from the [Mac AppStore](https://itunes.apple.com/app/funky/id1210707379) at [https://itunes.apple.com/app/funky/id1210707379](https://itunes.apple.com/app/funky/id1210707379).
+
+## Building
+
+Building should be straightforward, except for one little caveat: Funky is also distributed through the Mac AppStore, therefore it performs a [MAS receipt validation](https://developer.apple.com/library/archive/releasenotes/General/ValidateAppStoreReceipt/Introduction.html#//apple_ref/doc/uid/TP40010573-CH105-SW1). 
+
+This means that if you try to run a *release* build, it will fail to start as there is no actual Mac AppStore receipt present.
+
+In order to disable the check, simply set the `DEVELOPMENT` variable to `1`, either in the `main.m` file or through a compile-time define.
 
 ---
 
 ## Contributors Welcome
 
 Since my time is fairly limited, contributions are more than welcome to, well, *contribute*. If you think Funky is a useful tool and your macOS kung-fu is strong, feel free to fork and submit a pull request.
+
+## Privacy Policy
+
+Please carefully read the [Privacy Policy](https://github.com/thecatalinstan/Funky/blob/master/Privacy.md).