chore: fix broken links to XML spec and nanotdf spec

[damorris25]

fix broken links

• DNI.org link to XML spec
• link to nanotdf spec

Proposed Changes

Checklist

• [ ] A clear description of the change has been included in this PR.
• [ ] A clear description of whether this change is a Major, Minor, Patch or cosmetic change as per the Versioning Guidelines has been included in this PR.
• [ ] All schema validation tests have been updated appropriately and are passing.
• [ ] MAJOR/MINOR VERSION CHANGES ONLY: This PR should be made in branches prefixed with draft-<change>
• [ ] MAJOR/MINOR VERSION CHANGES ONLY: A link to a reference implementation (PR or set of PRs) of the change has been included in this PR.
• [ ] MAJOR/MINOR VERSION CHANGES ONLY: A writeup has been included discussing the motivation and impact of this change.
• [ ] MAJOR/MINOR VERSION CHANGES ONLY: The minimum wait time has elapsed.
• [ ] DRAFT MERGE ONLY: Draft Semver has been updated in the VERSION file (optional)
• [ ] DRAFT MERGE ONLY: Tagged this branch with new semver version and an annotation describing the change (ex: git tag -s 4.1.0 -m "Spec version 4.1.0 - did a thing")
• [ ] DRAFT MERGE ONLY: Version numbers have been updated as per the Versioning Guidelines.
• [ ] This change otherwise adheres to the project Contribution Guidelines.