Add code snippet for embeddings normalization

[Tengxin-Li]

Description

Add code snippet for embeddings normalization, so that the magnitude of the array is always 1.

Checklist

• [X] I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• [X] README is updated to include all relevant information
• [ ] Tests pass: nox -s py-3.9 (see Test Environment Setup)
• [X] Lint pass: nox -s lint (see Test Environment Setup)
• [ ] These samples need a new API enabled in testing projects to pass (let us know which ones)
• [ ] These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• [ ] This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• [ ] This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• [X] Please merge this PR for me once it is approved

[glasnt]

This PR appears to be failing on the change introduced in #13396. This may need to be reverted.