Update README.md

[blaiszik]

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[what-the-diff]

PR Summary

• ReadMe File URL Update
  This update corrects a URL in the documentation, specifically in the README. While the actual web address didn't change, we simply added a trailing space after the link. This may seem like a small thing, but it might prevent errors when copying and pasting the URL. Previously, it was https://www.materialsdatafacility.org and now it is https://www.materialsdatafacility.org (with an additional space at the end). This optimization ensures the link works as expected when users interact with the document.