Add RSS feed so folks can subscribe to the blogpost

[tcharding]

Currently the blog post is just static content generated by Hugo. It would be cool if folks could subscribe to get new posts.

[apoelstra]

My personal blog is static (generated by Pelican) and it has an RSS feed. So there's no reason in principle we can't do this.

[realeinherjar]

I don't know if you guys are aware, but this is already done today.

Nightfall theme generates RSS by default (check LordMathis/hugo-theme-nightfall#16).

If you go to https://rust-bitcoin.org/index.xml you'll see the feed.

Additionally, I've tested with my RSS reader. If you add https://rust-bitcoin.org it will find the RSS feed and render everything OK.
Here's a pic:

We can close this

[tcharding]

Gee, you are a useful bloke to have about @realeinherjar.