docs: clarify package.json override value specs

[ded-furby]

Summary

• state explicitly that override values accept standard npm dependency specifiers
• add a semver range example for override values
• keep the change scoped to the existing package.json#overrides docs

Closes#9475.

Validation

• git diff --check

[github-actions]

🎉 Backport to release/v11 created: #9508