docs: add import to getting started example (#8501)

docs/getting-started.md

@@ -29,6 +29,7 @@ $ yarn add tedious // MSSQL
 Sequelize will setup a connection pool on initialization so you should ideally only ever create one instance per database if you're connecting to the DB from a single process. If you're connecting to the DB from multiple processes, you'll have to create one instance per process, but each instance should have a maximum connection pool size of "max connection pool size divided by number of instances".  So, if you wanted a max connection pool size of 90 and you had 3 worker processes, each process's instance should have a max connection pool size of 30.
 
 ```js
+const Sequelize = require('sequelize');
 const sequelize = new Sequelize('database', 'username', 'password', {
   host: 'localhost',
   dialect: 'mysql'|'sqlite'|'postgres'|'mssql',