Renamed branch to main in links in README

[KiraBurova]

I renamed branch to main in links that are pointing to the .md files with docs inside the repo. The links were working but with "redirected to default branch" message, and I think this way it is cleaner :)

[vercel[bot]]

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployment, click below or on the icon next to each commit.

🔍 Inspect: https://vercel.com/sakhnyuk/rc-scrollbars/AkWDLDAABp3CSdoLszCUjio7S8yY
✅ Preview: https://rc-scrollbars-git-fork-kiraburova-fix-readme-links-sakhnyuk.vercel.app

[sakhnyuk]

Thank you 👍