Added Rootish Array Stack to Readme

Author: BenEmdon

README.markdown

@@ -130,6 +130,7 @@ Most of the time using just the built-in `Array`, `Dictionary`, and `Set` types
 - [Bit Set](Bit Set/). A fixed-size sequence of *n* bits.
 - [Fixed Size Array](Fixed Size Array/). When you know beforehand how large your data will be, it might be more efficient to use an old-fashioned array with a fixed size.
 - [Ordered Array](Ordered Array/). An array that is always sorted.
+- [Rootish Array Stack](Rootish Array Stack/). A space and time efficient variation on Swift arrays.
 
 ### Queues
 
@@ -205,6 +206,7 @@ The following books are available for free online:
 - [Algorithms, Etc.](http://jeffe.cs.illinois.edu/teaching/algorithms/) by Erickson
 - [Algorithms + Data Structures = Programs](http://www.ethoberon.ethz.ch/WirthPubl/AD.pdf) by Wirth
 - Algorithms and Data Structures: The Basic Toolbox by Mehlhorn and Sanders
+- [Open Data Structures](http://opendatastructures.org) by Pat Morin
 - [Wikibooks: Algorithms and Implementations](https://en.wikibooks.org/wiki/Algorithm_Implementation)
 
 Other algorithm repositories: