README.md: remove outdated Windows cache tip link

[me-and]

Description

As of 9b0be58 (Release compression related changes for windows (#1039), 2022-12-23), the section of tips-and-workarounds.md referring to improving cache restore performance on Windows no longer exists, so don't link to it from README.md.

Motivation and Context

See above: this is a small change to README.md to remove a link that's no longer needed.

How Has This Been Tested?

• GitHub Actions run of the test scripts at https://github.com/me-and/cache/actions/runs/3771529989
• Visual check of the rendering at https://github.com/me-and/cache/tree/correct-readme-re-windows#known-practices-and-workarounds

Screenshots (if appropriate):

Not applicable.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (add or update README or docs)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[lvpx]

Thank you for creating this issue @me-and.