Adding more explanation to the documentation

Adding code

There are three ways to contribute code: a snippet,
a dartpad, or a sample.
For more details, see the Dartdoc Generation README.

Please be cognizant that writing sample code has a different goal
(and some additional constraints) compared to writing production code.
Mozilla has a good overview (the article is about the web,
but 95% of it applies to any platform).

Snippets

Snippets can be added using the following syntax:

/// {@tool snippet}

///

/// This is a comment explaining the snippet below:

///

/// ```dart

/// MyWidget(

///   color: Colors.green,

/// )

/// ```

/// {@end-tool}

Sample