Improved readme (#23079)
Improved readme (#23079)

Link to CONTRIBUTING.md in the flutter_tools README

tvolkert/flutter,cbracken/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,Hixie/flutter