Explicit title image caption

[xaur]

Shall we place the image info under the image or leave it as tooltip (kind of an Easter egg)?

Demo:

https://github.com/xaur/decred-news/blob/poc/titleimage/journal/201905.md

[xaur]

So we tried it in production in June 2019. We went with a short title of image title and credit because I could not figure out text that would either make sense or be abstract enough to not need that claim.

On Medium it is grayed and centered, looks cool imo. On GitHub Pages it looks allright.

Still thinking about the nits (whether to quote the title and place period at the end) but in general it finally looks right. These images deserve more exposure.