As per Documents 

Error: No pubspec.yaml file found.

This command should be run from the root of your Flutter project.

Do not run this command from the root of your git clone of Flutter.

if you still getting this type of error 

then 

Looks like you are running flutter run command from a different directory (maybe parent directory).

Try running flutter run command from the project directory. 

To solve this error in the EASIEST WAY follows the below steps:

1. Go to terminal
2. Then find local tabs
3. Then click on a '+' sign and type your command.

This should solve your error