[Readme] Adds readme. Fixes #3.

README.md

@@ -1,3 +1,42 @@
 # RxNimble
 
 Nimble extensions that making unit testing with RxSwift easier :tada:
+
+## Why
+
+RxSwift includes a really nifty little library called [RxBlocking](http://cocoapods.org/pods/RxBlocking) which provides convenience functions for peeking in on `Observable` instances. Check is a *blocking call*, hence the name. 
+
+But writing code to check an `Observable`'s value is sooooo tedious:
+
+```swift
+let result = try! observabe.toBlocking().first()
+expect(result) == 42
+```
+
+With `RxNimble`, we've added [Nimble](https://github.com/Quick/Nimble) matchers for `Observable`s, so the code above can be rewritten as:
+
+```swift
+expect(observable) == 42
+```
+
+Nice.
+
+## Installation
+
+Add to your podfile:
+
+```rb
+pod 'RxNimble'
+```
+
+And `pod install` and that's it!
+
+## Known Issues
+
+Very very _very_ rarely the Swift compiler gets confused about the different types and you need to use the original `RxBlocking` code.
+
+## License
+
+MIT ofc.
+
+![Give yourself a high five](https://media.giphy.com/media/dRkMyTvCuAdY4/giphy.gif)