[FEATURE REQUEST] Add warning if config file isnt located next to pubspec.yaml directory

[apgapg]

💬 Description

I placed all my launcher icon config files in a dir named launcher_icon/ due to which flavors weren't respected.
After struggle, I saw a note in README to place it within the same dir as of pubspec.yaml.

Can we add a warning in console stating to put config file besides pubspec so as to prevent errors for future developers?

[timbrueckner]

I think, this issue was fixed with #398. If the plugin does not find a config file, it now hints to use the --file option in order to point to the config.

✗ ERROR: NoConfigFoundException
No configuration found in flutter_launcher_icons.yaml or in pubspec.yaml. In case file exists in different directory use --file option