docs: bump minSdk to 23 (facebook#42034)

Summary:
The Android minSdk has been bumped in facebook#38874 but not in the README.

## Changelog:
[General] [Fixed] - Updated docs to match Android 6.0 (API 23) minimum requirement.

Pull Request resolved: facebook#42034

Test Plan: N/A

Reviewed By: fkgozali

Differential Revision: D52364522

Pulled By: arushikesarwani94

fbshipit-source-id: b04b5aa94b629380b559b2717e12a882f8817a6f

README.md

@@ -67,7 +67,7 @@ React Native is developed and supported by many companies and individual core co
 
 ## 📋 Requirements
 
-React Native apps may target iOS 13.4 and Android 5.0 (API 21) or newer. You may use Windows, macOS, or Linux as your development operating system, though building and running iOS apps is limited to macOS. Tools like [Expo](https://expo.dev) can be used to work around this.
+React Native apps may target iOS 13.4 and Android 6.0 (API 23) or newer. You may use Windows, macOS, or Linux as your development operating system, though building and running iOS apps is limited to macOS. Tools like [Expo](https://expo.dev) can be used to work around this.
 
 ## 🎉 Building your first React Native app