Update How to Contribute link

Super simple but just something I noticed while getting started.
Cheers!

Author: kevinvanderlugt

README.markdown

@@ -227,7 +227,7 @@ The Swift Algorithm Club was originally created by [Matthijs Hollemans](https://
 
 It is now maintained by [Vincent Ngo](https://www.raywenderlich.com/u/jomoka) and [Kelvin Lau](https://github.com/kelvinlauKL).
 
-The Swift Algorithm Club is a collaborative effort from the [most algorithmic members](https://github.com/rwenderlich/swift-algorithm-club/graphs/contributors) of the [raywenderlich.com](https://www.raywenderlich.com) community. We're always looking for help - why not [join the club](How to Contribute.markdown)? :]
+The Swift Algorithm Club is a collaborative effort from the [most algorithmic members](https://github.com/rwenderlich/swift-algorithm-club/graphs/contributors) of the [raywenderlich.com](https://www.raywenderlich.com) community. We're always looking for help - why not [join the club](How%20to%20Contribute.markdown)? :]
 
 ## License