Circular dependencies on polymer paper elements

[yosefsun]

Since Polymer elements are commonly used when integrating Polymer, it's worth mentioning here that paper elements a likely to cause circular dependencies issues (that's what happened to me until I realized the segmentation fault was caused by dependency issues ;) ).

If you would like to use paper elements, I suggest you will use the paper-elements-rails gem referenced here.

@alchaplinsky should you add that warning on the readme page? (same way you did with polymer-paper-elements here).

hope that helps.