Update OMB Memorandum link that was no longer available (404)

[geekygirlsarah]

The link to the OMB memorandum is no longer available in the README. I found two archived copies:

• https://www.whitehouse.gov/wp-content/uploads/legacy_drupal_files/omb/memoranda/2017/m-17-06.pdf
• https://obamawhitehouse.archives.gov/sites/default/files/omb/memoranda/2017/m-17-06.pdf

While both would be fine to replace the link with, I went with the archives.gov as I felt it was least likely to have it's directory structure moved or replaced in the future (though would be happy to replace it with the whitehouse.gov legacy_drupal_files one).

Thanks for reviewing!

[geekygirlsarah]

Pinging to bring this up to someone's attention.

[smarina04]

Thank you, updated.