DAS plugins: Write initial text for README

Change-Id: I97aee31ed59a136591c71fc36d6f3febc9a53b18
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/450800
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>

Author: srawlins

pkg/analysis_server_plugin/README.md

@@ -1,8 +1,30 @@
 # analysis\_server\_plugin package
 
-This package offers support for writing Dart analyzer plugins.
+This package offers support for writing Dart analysis server plugins.
 
-Until this README is fleshed out, more inforamtion can be found in the [docs][].
+Analysis server plugins empower developers to contribute their own Dart static
+analysis in IDEs and at the command line via `dart analyze` and `flutter
+analyze`. Analysis server plugins can offer the following static analyses:
 
-[docs]: https://github.com/dart-lang/sdk/tree/main/pkg/analysis_server_plugin/doc
+* analysis rules, which report diagnostics in the IDE, and at the command line
+* IDE quick fixes, which are local refactorings offered to users to correct a
+  given diagnostic
+* IDE quick assists, which are local refactorings that are offered at specific
+  syntax nodes in code, but do not necessarily correct a static code issue
 
+Review the following documents for how to write and how to use analysis server
+plugins:
+
+* [Writing a plugin][]
+  * [Writing rules][]
+  * [Testing rules][]
+  * [Writing fixes][]
+  * [Writing assists][]
+* [Using plugins][]
+
+[Writing a plugin]: https://github.com/dart-lang/sdk/tree/main/pkg/analysis_server_plugin/doc/writing_a_plugin.md
+[Writing rules]: https://github.com/dart-lang/sdk/tree/main/pkg/analysis_server_plugin/doc/writing_rules.md
+[Testing rules]: https://github.com/dart-lang/sdk/tree/main/pkg/analysis_server_plugin/doc/testing_rules.md
+[Writing fixes]: https://github.com/dart-lang/sdk/tree/main/pkg/analysis_server_plugin/doc/writing_fixes.md
+[Writing assists]: https://github.com/dart-lang/sdk/tree/main/pkg/analysis_server_plugin/doc/writing_assists.md
+[Using plugins]: https://github.com/dart-lang/sdk/tree/main/pkg/analysis_server_plugin/doc/using_plugins.md