Fix broken demo link in readme (#3440)
Fix broken demo link in readme (#3440)

* Fix broken demo link in readme

added links to 2 demos for iOS and macOS

* Update README.md

* Update README.md

danielgindi/Charts,FreddyZeng/Charts,liuxuan30/ios-charts,FreddyZeng/Charts,liuxuan30/Charts,jum/Charts,FreddyZeng/Charts,jjatie/Charts,danielgindi/ios-charts,MAARK/Charts,jjatie/Charts,liuxuan30/Charts,liuxuan30/Charts,FreddyZeng/Charts,jjatie/Charts,danielgindi/ios-charts,liuxuan30/ios-charts,icecrystal23/ios-charts,MAARK/Charts,liuxuan30/ios-charts,liuxuan30/ios-charts,MAARK/Charts,danielgindi/ios-charts,liuxuan30/Charts,icecrystal23/ios-charts,MAARK/Charts,danielgindi/ios-charts,icecrystal23/ios-charts,icecrystal23/ios-charts,danielgindi/Charts,danielgindi/Charts,jum/Charts,danielgindi/Charts,jum/Charts,jjatie/Charts,jum/Charts