Fix broken anchors in readme and docs index (#11338)
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## Summary
I've just fixed some broken anchors after browing ux doc site.
## Test Plan
- `index.md`: based on `mkdocs serve` log
- `readme.md`: manual check
## Aside
Do you manually keep `readme.md` and `index.md` partially sync? I've
tried
checking pre-commit and other scripts but found no way to port my edits
from one
to the other.
<!-- How was it tested? -->
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Co-authored-by: Zanie Blue <contact@zanie.dev>
