Added tutorial link back in with new URL as provided by @DarrenN

Author: peter-mcconnell

speech_recognition/README.md

@@ -2,6 +2,8 @@
 
 ## External Papers
 
+[A tutorial on hidden Markov models and selected applications in speech recognition](http://luthuli.cs.uiuc.edu/~daf/courses/Signals%20AI/Papers/HMMs/0.pdf)
+
 [Weighted Finite-State Transducers in Speech Recognition](http://www.cs.nyu.edu/~mohri/pub/csl01.pdf)
 
 [Decoding speech in the presence of other sources](http://www.ee.columbia.edu/~dpwe/pubs/BarkCE05-sfd-spcomm.pdf)