Add logic to detect out of date translations

[stgraber]

We should automatically print a header warning with a link to the english version when the matching translated markdown file is older than the source english version.

[anirudh-goyal]

Hello, I'm a CS student at UT Austin. I was wondering if me and my classmates could work on this issue as part of our virtualization class? Thank you!

[stgraber]

Absolutely, assigning to you!