Merge pull request #37 from griffithlab/leanpub-fix

update Book.txt to current set of chapters

Author: obigriffith

Book.txt

@@ -1,8 +1,10 @@
 About-this-Course.md
 1-Introduction.md
-2-Running-pVACtools.md
-3-Tour-of-pVACview.md
-4-Conclusions.md
+2-Prerequisites.md
+3-Running-pVACtools.md
+4-Understanding-pVACtools-outputs.md
+5-Review-Your-Results-in-pVACview.md
+6-Conclusions.md
 quiz_1.md
-5-References.md
+7-References.md
 About-the-Authors.md