chore: update app description and increment version to 1.0.0+20 in pubspec.yaml

pubspec.yaml

···
 name: grain
-description: "A new Flutter project."
+description: "Grain Social Mobile App"
 # The following line prevents the package from being accidentally published to
 # pub.dev using `flutter pub publish`. This is preferred for private packages.
 publish_to: "none" # Remove this line if you wish to publish to pub.dev
···
 # https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
 # In Windows, build-name is used as the major, minor, and patch parts
 # of the product and file versions while build-number is used as the build suffix.
-version: 1.0.0+19
+version: 1.0.0+20
 
 environment:
   sdk: ^3.8.1