docs: Add demo video

[Dhruv-Varshney-developer]

Objective:

Create a beginner-friendly demo video to make it easy for anyone (especially those new to Storacha and UCANs) to understand, run, and extend this demo by taking this repository as a boilerplate code.

🎥 Demo Video Requirements:

• Quick walkthrough of the codebase.

• Show how UCANs are generated and verified.

• Showcase Storacha integration (file upload, storage etc).

• Demonstrate full app flow: upload → share → access → revoke.

• Keep it clear and concise.

Reference links:

1. https://medium.com/@storacha/spicing-up-access-a-saucy-guide-to-storacha-delegations-%EF%B8%8F-afda976f99f8
2. https://docs.storacha.network/concepts/ucans-and-storacha
3. https://github.com/storacha/w3up-examples/
4. https://github.com/storacha/ucanto
5. https://www.youtube.com/@StorachaNetwork/videos

Note: PR for this issue can be merged only after all features are completed.

[Dhruv-Varshney-developer]

As communicated over Discord, taking this up due to a lack of progress here. Please take up new issues from docusign storacha repository.
Thanks for your efforts.