typo: Update README.md

[Kiruel]

Typo fix on README.

Pre-launch Checklist

• [ ] I made sure the project builds.
• [ ] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [ ] I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is does not need version changes.
• [ ] I updated CHANGELOG.md to add a description of the change.
• [ ] I updated/added relevant documentation (doc comments with ///).
• [ ] I rebased onto main.
• [ ] I added new tests to check the change I am making, or this PR does not need tests.
• [ ] I made sure all existing and new tests are passing.
• [ ] I ran dart format . and committed any changes.
• [ ] I ran flutter analyze and fixed any errors.