[readme] fix links in root markdown (#1964)

README.md

@@ -31,7 +31,7 @@ don't naturally belong to other topic monorepos (like
 | [html](pkgs/html/) | APIs for parsing and manipulating HTML content outside the browser. | [![package issues](https://img.shields.io/badge/package:html-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Ahtml) | [![pub package](https://img.shields.io/pub/v/html.svg)](https://pub.dev/packages/html) |
 | [io](pkgs/io/) | Utilities for the Dart VM Runtime including support for ANSI colors, file copying, and standard exit code values. | [![package issues](https://img.shields.io/badge/package:io-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Aio) | [![pub package](https://img.shields.io/pub/v/io.svg)](https://pub.dev/packages/io) |
 | [json_rpc_2](pkgs/json_rpc_2/) | Utilities to write a client or server using the JSON-RPC 2.0 spec. | [![package issues](https://img.shields.io/badge/package:json_rpc_2-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Ajson_rpc_2) | [![pub package](https://img.shields.io/pub/v/json_rpc_2.svg)](https://pub.dev/packages/json_rpc_2) |
-| [markdown](pkgs/markdown/) | A portable Markdown library written in Dart that can parse Markdown into HTML. | [![pub package](https://img.shields.io/pub/v/markdown.svg)](https://pub.dev/packages/markdown) |
+| [markdown](pkgs/markdown/) | A portable Markdown library written in Dart that can parse Markdown into HTML. | [![package issues](https://img.shields.io/badge/package:markdown-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Amarkdown) | [![pub package](https://img.shields.io/pub/v/markdown.svg)](https://pub.dev/packages/markdown) |
 | [mime](pkgs/mime/) | Utilities for handling media (MIME) types, including determining a type from a file extension and file contents. | [![package issues](https://img.shields.io/badge/package:mime-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Amime) | [![pub package](https://img.shields.io/pub/v/mime.svg)](https://pub.dev/packages/mime) |
 | [oauth2](pkgs/oauth2/) | A client library for authenticating with a remote service via OAuth2 on behalf of a user, and making authorized HTTP requests with the user's OAuth2 credentials. | [![package issues](https://img.shields.io/badge/package:oauth2-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Aoauth2) | [![pub package](https://img.shields.io/pub/v/oauth2.svg)](https://pub.dev/packages/oauth2) |
 | [package_config](pkgs/package_config/) | Support for reading and writing Dart Package Configuration files. | [![package issues](https://img.shields.io/badge/package:package_config-4774bc)](https://github.com/dart-lang/tools/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Apackage_config) | [![pub package](https://img.shields.io/pub/v/package_config.svg)](https://pub.dev/packages/package_config) |