When contributing content, please only make your changes in the markdown files
under the _src directory. The person merging your pull request will deal with
re-generating the html files at the root of the repo.
If your contribution touches example code inside a ```rust code
block which has a !PLAYGROUND on the previous line, the hash on that line
needs to be updated by pasting the new code into play.rust-lang.org, clicking
Share, and grabbing the new hash from the generated "Permalink to the
playground" link.