Added extra item under systems design.

README.md

@@ -853,9 +853,11 @@ You'll get more graph practice in Skiena's book (see Books section below) and th
     - [x] https://github.com/checkcheckzz/system-design-interview - There are a lot of resources in this one. Look through the articles and examples. I put some of them below.
     - [x] How to ace a systems design interview: http://www.palantir.com/2011/10/how-to-rock-a-systems-design-interview/
     - [x] Scalable Web Architecture and Distributed Systems: http://www.aosabook.org/en/distsys.html
-    - [ ] Numbers Everyone Should Know: http://everythingisdata.wordpress.com/2009/10/17/numbers-everyone-should-know/
-    - [ ] Fallacies of Distributed Computing Explained: https://pages.cs.wisc.edu/~zuyu/files/fallacies.pdf
-    - [ ] Pragmatic Programming Techniques: http://horicky.blogspot.com/2010/10/scalable-system-design-patterns.html
+    - [x] Numbers Everyone Should Know: http://everythingisdata.wordpress.com/2009/10/17/numbers-everyone-should-know/
+    - [x] How long does it take to make a context switch?: http://blog.tsunanet.net/2010/11/how-long-does-it-take-to-make-context.html
+    - [x] Fallacies of Distributed Computing Explained: https://pages.cs.wisc.edu/~zuyu/files/fallacies.pdf
+    - [x] Pragmatic Programming Techniques: http://horicky.blogspot.com/2010/10/scalable-system-design-patterns.html
+        - extra: Google Pregel Graph Processing: http://horicky.blogspot.com/2010/07/google-pregel-graph-processing.html
     - [ ] Introduction to Architecting Systems for Scale: http://lethain.com/introduction-to-architecting-systems-for-scale/
     - [ ] Transactions Across Datacenters: https://www.youtube.com/watch?v=srOgpXECblk
     - [ ] A plain english introduction to CAP Theorem: http://ksat.me/a-plain-english-introduction-to-cap-theorem/