增加引入说明

README.md

-# app_base_repository
-
-A new Flutter package project.
-
-## Getting Started
-
-This project is a starting point for a Dart
-[package](https://flutter.dev/developing-packages/),
-a library module containing code that can be shared easily across
-multiple Flutter or Dart projects.
-
-For help getting started with Flutter, view our 
-[online documentation](https://flutter.dev/docs), which offers tutorials, 
-samples, guidance on mobile development, and a full API reference.
+# 引入方法
+
+```
+base_repository:
+    git:
+        url: 'git@git.xiaomanxiong.com:flutter-plugin/app-base-repository.git'
+        ref: 'null-safety'
+```