[connectivity] update the connectivity readme to include info about changes in iOS 13

[danwulff]

Description

Update the Readme for the Connectivity plugin to include information about changes in iOS 13.

Specifically the tightening of security around SSID and BSSID information.

Apple's email announcing the change:

Apple's documentation about CNCopyCurrentNetworkInfo

Related Issues

Resolves: #35322

A followup issue has been created for "fixing" the iOS 13 functionality at #37804

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• [ X ] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• [ X ] All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• [ X ] The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• [ X ] I signed the CLA.
• [ X ] I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• [ X ] No, this is not a breaking change.

[danwulff]

@cyanglaz Do I also need to increment the package version and add to the changelog, since it's just a readme change?

[cyanglaz]

Thank you very much for this! It is a really nice starting point.
I left some comments, and we also need to update the pubspec and changelog to a new version so we can publish this readme to pub

[cyanglaz]

@danwulff Also, I think the fix you mentioned in flutter/flutter#37804 with the location request is pretty straightforward. If you want to include the fix in a same PR I'm happy to review it too.

[danwulff]

@cyanglaz I would love to make the code changes as well, but I don't have the ability to test with iOS 13 currently.

Will make changes per your suggestions by end of day.

[cyanglaz]

@danwulff That's great! Thanks! There is no rush, please take your time :)

[danwulff]

@cyanglaz Let me know if you see any other changes that need to happen.

[cyanglaz]

@danwulff Can we include the fixes in this same PR?

[danwulff]

@cyanglaz I can't sorry. I don't have the capability of using Xcode 11 (iOS 13 SDK).

If you or another googler want to add on to this PR feel free.

[cyanglaz]

@danwulff Oh, sorry i didn't read your last comment clearly. That's ok.

@cyanglaz I can't sorry. I don't have the capability of using Xcode 11 (iOS 13 SDK).

If you or another googler want to add on to this PR feel free.

Looks good! Going to merge when green.