replace paywalled with public version

Reconstructing human contributions to accidents paper is available on Dekker's website

intro.md

@@ -80,9 +80,9 @@ Johan Bergström of Lund University has three excellent short (<10 minute) video
 * [Three analytical traps in accident investigation](https://www.youtube.com/watch?v=TqaFT-0cY7U)
 * [Two views on human error](https://www.youtube.com/watch?v=rHeukoWWtQ8)
 
-Two great introductory papers (alas, both paywalled) are:
+Two great introductory papers (alas, 2nd one is paywalled) are:
 
-* [Reconstructing human contributions to accidents: the new view on error and performance](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.411.4985&rep=rep1&type=pdf) 
+* [Reconstructing human contributions to accidents: the new view on error and performance](http://sidneydekker.stackedsite.com/wp-content/uploads/sites/899/2013/01/SafetyResearch.pdf) 
 by Dekker 
 * [The error of counting errors](https://doi.org/10.1016/j.annemergmed.2008.03.015) by Robert Wears