Improved the iOS Setup section in permission_handler/README.md

[Hemo-Sul]

After version 8.0.0, permission_handler no longer uses all permissions on iOS (only required permissions selected by the developers) but this was not explained clearly in the README. Due to this, I struggled for a few hours to understand how to setup the permissions properly, but eventually I solved my problem after searching through older issues. I think it is quite necessary to improve the documentation so that future developers won't have to go through this.

Fixed this issue, which can be closed now: #1170

Note: This is only a minor document improvement, I did not change any code at all

P.S. I have no idea why the check failed, I did literally nothing to the code ;-;

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.