How to use commnents in Dart code?

[SimonLab]

Add a section in README to describe how to use comments in Dart code

• line comment with //
• block comment /*...*/
• documentation comment with ///. Can be useful with dartdoc which is a tool to convert doc comment to html. Markdown format can be used in doc comment

ref: https://dart.dev/guides/language/effective-dart/documentation