Added reference for context switching, and new source (Unix internals book, McKusick)

bibliography.bib

@@ -235,4 +235,10 @@
     title = {{IEEE 90: IEEE Standard Glossary of Software Engineering Terminology}},
     year = {1990}
 }
-
+@book{McKusick:2004:DIF:1014910,
+ author = {McKusick, Marshall Kirk and Neville-Neil, George V.},
+ title = {The Design and Implementation of the FreeBSD Operating System},
+ year = {2004},
+ isbn = {0201702452},
+ publisher = {Pearson Education},
+}