* add documentation to files

* Update dev/conductor/core/lib/src/stdio.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

* Update dev/conductor/core/lib/src/start.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

* Update dev/conductor/core/lib/src/repository.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

* Update dev/conductor/core/lib/src/next.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

* Update dev/conductor/core/lib/src/git.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

* Update dev/conductor/core/lib/src/git.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

* Update stdio.dart

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Co-authored-by: Christopher Fujino <fujino@google.com>