Fixes #6271 - add var convention to Bastion readme

The readme was missing information about our convention of declaring vars at the top of a function.

http://projects.theforeman.org/issues/6271
I wanted to get across that you can make the assignment at the same time as declaring the `var`, not the single line vs. stacking.  That's a good thing to add though.

How about:

"Declare all `var` statements at the top of a function in order to prevent problems associated with variable hoisting. It is okay to declare and assign `var` statements simultaneously.  We prefer stacking `var` statements for readability."

And change the actual example to be stacked.