fix(shorebird_cli): improve shorebird init missing pubspec.yaml error (#169)

packages/shorebird_cli/lib/src/commands/init_command.dart

@@ -30,7 +30,10 @@ class InitCommand extends ShorebirdCommand
     final progress = logger.progress('Initializing Shorebird');
     try {
       if (!hasPubspecYaml) {
-        progress.fail('Could not find a "pubspec.yaml".');
+        progress.fail('''
+Could not find a "pubspec.yaml".
+Please make sure you are running "shorebird init" from the root of your Flutter project.
+''');
         return ExitCode.noInput.code;
       }
     } catch (error) {

packages/shorebird_cli/test/src/commands/init_command_test.dart

@@ -72,7 +72,14 @@ environment:
         command.run,
         getCurrentDirectory: () => tempDir,
       );
-      verify(() => progress.fail('Could not find a "pubspec.yaml".')).called(1);
+      verify(
+        () => progress.fail(
+          '''
+Could not find a "pubspec.yaml".
+Please make sure you are running "shorebird init" from the root of your Flutter project.
+''',
+        ),
+      ).called(1);
       expect(exitCode, ExitCode.noInput.code);
     });