Update examples/stable_diffusion/README.md

[snnn]

Describe your changes

Update ONNX Runtime's installation instructions

Checklist before requesting a review

• [N/A ] Add unit tests for this change.
• [N/A ] Make sure all tests can pass.
• Update documents if necessary.
• [N/A ] Lint and apply fixes to your code by running lintrunner -a
• [ N/A] Is this a user-facing change? If yes, give a description of this change to be included in the release notes.
• [ N/A] Is this PR including examples changes? If yes, please remember to update example documentation in a follow-up PR.

(Optional) Issue link

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