Fence the code with shell formatting

Author: holman

README.md

@@ -9,7 +9,9 @@ spark is a [shell script][bin], so drop it somewhere and make sure it's added
 to your `$PATH`. It's helpful if you have a super-neat collection of dotfiles,
 [like mine][dotfiles]. Or you can use the following one-liner:
 
-    sudo sh -c "curl https://raw.githubusercontent.com/holman/spark/master/spark -o /usr/local/bin/spark && chmod +x /usr/local/bin/spark"
+```sh
+sudo sh -c "curl https://raw.githubusercontent.com/holman/spark/master/spark -o /usr/local/bin/spark && chmod +x /usr/local/bin/spark"
+```
 
 If you're on OS X, spark is also on [Homebrew][brew]: