chore: add supported platforms description

[marandaneto]

💡 Motivation and Context

wrong repo

💚 How did you test it?

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

[github-actions]

	Fails
🚫	Please consider adding a changelog entry for the next release.

Instructions and example for changelog

Please add an entry to CHANGELOG.md to the "Next" section. Make sure the entry includes this PR's number.
Example:

## Next
- add supported platforms description ([#105](https://github.com/PostHog/posthog-ios/pull/105))

If none of the above apply, you can opt out of this check by adding #skip-changelog to the PR description.

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