docs: link use package references

[aose-yuu]

Purpose

Make the core README references to @sigrea/use easier to follow from npm and GitHub.

Summary

• Links the install note for @sigrea/use to the npm package.
• Links the createEvents mention in the controlled-value example to the use package docs.
• Converts npm-broken contributing links to GitHub URLs.
• Wraps long README prose around sentence and clause boundaries.

Verification

• pnpm -s cicheck
• git diff --check