Merge pull request #107 from massysett/master

Add text to tutorial describing the Stack shebang line

src/Turtle/Tutorial.hs

@@ -33,6 +33,14 @@
 
 > $ stack install turtle
 
+    The first two lines of each script below contain boilerplate instructions
+    so that `stack` will load and run the script.  This helps ensure that a
+    script will run on any computer that has a `stack` executable, as `stack`
+    can install a Haskell compiler if one is not already present.
+    If you are curious about how these two lines work, they are described here:
+
+    <https://github.com/commercialhaskell/stack/blob/master/doc/GUIDE.md#ghcrunghc>
+
 -}
 
 module Turtle.Tutorial (