auto build gallery on PR merge

[bburns632]

Recently, @jameslamb generously contributed #28 by following our readme page. However, that does not automatically rebuild the website to make his contribution visible. #29 was needed for that.

So far, that has been a purposeful decision (eyeball the website before pushing). At some point soon, we should be able to trust the process enough to automatically rebuild the html from the .rmd file upon merge, perhaps with the addition of a few key unit tests.

[jameslamb]

ignore the comment I just made on #29 haha, thanks for opening this issue!

[bburns632]

.github/workflows/ does not yet do that automatically but it does make it button push automated.