[packaging-on-the-web] Vary header use (#16)

In the examples `Vary` is used alongside HTTP response headers. [`Vary`](http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.44) is defined to work with request headers as a value, so I'm not sure how that can work.

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Reply to this email directly or view it on GitHub:
https://github.com/w3ctag/packaging-on-the-web/issues/16