Add Polymer

[tpanetti]

You should definitely add Polymer, I'm willing to help contribute!

[feimosi]

Hi! The idea sounds really cool, but I wanted to keep the comparison with a limited number of frameworks. In the current 'everything-in-readme.md' approach it doesn't scale well and every new frameworks makes it harder to browse.
When I come up with a better approach (e.g. Gitbook) then you can freely add Polymer!