Update 'README.md'

README.md

@@ -1,2 +1,31 @@
 # flask-migrate
+数据库迁移管理。，创建、更新和删除表格、字段等。
 
+## Usage
+
+```
+from flask import Flask
+from flask_sqlalchemy import SQLAlchemy
+from flask_migrate import Migrate
+
+app = Flask(__name__)
+app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///app.db'
+db = SQLAlchemy(app)
+migrate = Migrate(app, db)
+
+class User(db.Model):
+    id = db.Column(db.Integer, primary_key=True)
+    username = db.Column(db.String(80), unique=True, nullable=False)
+    email = db.Column(db.String(120), unique=True, nullable=False)
+
+if __name__ == '__main__':
+    app.run()
+
+```
+
+```
+flask db init
+flask db migrate -m "initial migration"
+flask db upgrade
+
+```