Add dartdoc_test package to README.md package list (#264)

Author: ktanaka101

README.md

@@ -18,6 +18,7 @@ which can be reused independently.
 | [acyclic_steps](acyclic_steps/) | An explicit acyclic step dependency framework with concurrent evaluation and dependency injection. | [![pub package](https://img.shields.io/pub/v/acyclic_steps.svg)](https://pub.dev/packages/acyclic_steps) |
 | [canonical_json](canonical_json/) | Encoder and decoder for a canonical JSON format, useful when cryptographically hashing or signing JSON objects. | [![pub package](https://img.shields.io/pub/v/canonical_json.svg)](https://pub.dev/packages/canonical_json) |
 | [chunked_stream](chunked_stream/) | Utilities for working with chunked streams, such as byte streams which is often given as a stream of byte chunks with type `Stream<List<int>>`. | [![pub package](https://img.shields.io/pub/v/chunked_stream.svg)](https://pub.dev/packages/chunked_stream) |
+| [dartdoc_test](dartdoc_test/) | Utilities for testing code snippets embedded in documentation comments. | [![pub package](https://img.shields.io/pub/v/dartdoc_test.svg)](https://pub.dev/packages/dartdoc_test) |
 | [http_methods](http_methods/) | List of all HTTP methods registered with IANA as list of strings, and metadata such as whether a method idempotent. | [![pub package](https://img.shields.io/pub/v/http_methods.svg)](https://pub.dev/packages/http_methods) |
 | [neat_cache](neat_cache/) | A neat cache abstraction for wrapping in-memory or redis caches. | [![pub package](https://img.shields.io/pub/v/neat_cache.svg)](https://pub.dev/packages/neat_cache) |
 | [neat_periodic_task](neat_periodic_task/) | Auxiliary classes for reliably running a periodic task in a long-running process such as web-server. | [![pub package](https://img.shields.io/pub/v/neat_periodic_task.svg)](https://pub.dev/packages/neat_periodic_task) |