Update README.md

[Views2k]

Update the README gameplay demonstration link to the replacement video.

• The change is within the approved scope.
• The change improves usability, functionality, feel, reliability, or maintenance, or fixes a verified bug.
• I have read and agree to the contributor-rights terms in CONTRIBUTING.md.
• Regression coverage has been added or updated where appropriate.
• The complete Release test suite passes.
• No credentials, personal data, machine paths, game binaries, save data, private captures, or generated output are included, except matching shader bytecode for an approved shader change described in docs/SHADERS.md.
• User-facing changes are recorded in CHANGELOG.md.
• Native HUD assets are unchanged, or their distribution rights, provenance, and hashes are documented.