Update README.md

Fixes https://github.com/dart-lang/lints/issues/15

Author: mit-mit

README.md

@@ -1,5 +1,46 @@
 [![pub package](https://img.shields.io/pub/v/lints.svg)](https://pub.dev/packages/lints)
 [![Build Status](https://github.com/dart-lang/lints/workflows/validate/badge.svg)](https://github.com/dart-lang/lints/actions?query=branch%3Amain)
 
-This repo contains official Dart lint rules.
+# Official Dart lint rules.
 
+The Dart linter is a static analyzer for identifying possible problems in your
+Dart source code. More than a hundred [linter rules][rules] are available,
+checking anything from potential typing issues, coding style, and formatting.
+
+The current `package:lints` contains the official selections of lints that the
+Dart team encourages using.
+
+Two sets of lints are available:
+
+* ***Core lints***: Lints that help identify critical issues that are likely to
+lead to problems when running or consuming Dart code. All code should pass these
+lints.
+
+* ***Recommended lints***: Lints that help identify additional issues that may
+to lead to problems when running or consuming Dart code, and lints that enforce
+writing Dart using a single, ideomatic style and format. All code is encouraged
+to pass these lints. The recommended lints include all the core lints.
+
+## How these lints are used
+
+When creating new Dart project using the [`dart create`][dart create] command,
+the 'recommended' set of lints are enabled by default.
+
+When uploading a package to the [pub.dev] package repository, packages [are
+scored pub point][scoring] depending on whether they pass at least the 'core'
+lints (note: the recommended lints automatically include all core lints). 
+
+For documentation on the individual lints, see the [Linter rules][rules] page on
+dart.dev.
+
+## Customizing the pre-defined lint sets
+
+You can customize the pre-defined lint sets, both to disable one or more of the
+lints included, or to add additional lints. For details see [customizing static
+analysis].
+
+[dart create]: https://dart.dev/tools/dart-tool
+[scoring]: https://pub.dev/help/scoring
+[customizing static analysis]: https://dart.dev/guides/language/analysis-options
+[rules]: https://dart.dev/tools/linter-rules
+[pub.dev]: https://pub.dev