Link to RSS feed for Blog

[jducoeur]

Followup to #392 -- now that the RSS feed is working again, we should make it more readily findable.

Site design isn't my strong suit, but I would guess that we want a link around the top of the Blog page, with some version of the standard RSS icon (I have a Noun Project Pro membership, so I think I could use one of their versions if we like any of them), and text saying something obvious like "RSS".

[rossabaker]

I get it in my location bar because I have an RSS extension in Firefox. I don't know what's fashionable now that RSS isn't fashionable.