[CHANGELOG.md] Hyperlinks to issues and pull requests

[rlei-weta]

Hello,

Would it be possible for the CHANGELOG.md's Issue and PR references to become hyperlinks (they're consistently formatted for the most part!)

This would improve the change log browsing experience for developers interested in the code changes and discussions as part of the issue / PR. A nice to have really :)

... and, cheers to Pixar's USD team for providing clear & concise change logs every release.

[jilliene]

Filed as internal issue #USD-6421

[c64kernal]

Thanks for the sug, it's a good idea!