docs: update index.md to include all possible types of ads in docs

[psnet]

Description

update index.md to include all possible types of ads in docs

Release Summary

update index.md to include all possible types of ads in docs

Checklist

• I read the Contributor Guide
  and followed the process outlined there for submitting PRs.
  • Yes
• My change supports the following platforms;
  • Android
  • iOS
• My change includes tests;
  • e2e tests added or updated in __tests__e2e__
  • jest tests added or updated in __tests__
• I have updated TypeScript types that are affected by my change.
• This is a breaking change;
  • Yes
  • No

Test Plan

---

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[docs-page]

To view this pull requests documentation preview, visit the following URL:

docs.page/invertase/react-native-google-mobile-ads~765

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[CLAassistant]

All committers have signed the CLA.

[mikehardy]

🎉 This PR is included in version 15.4.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀