docs(connection): document Connection#models property

Fix #8314

Author: vkarpov15

lib/connection.js

@@ -187,6 +187,27 @@ Connection.prototype.collections;
 
 Connection.prototype.name;
 
+/**
+ * A [POJO](https://masteringjs.io/tutorials/fundamentals/pojo) containing
+ * a map from model names to models. Contains all models that have been
+ * added to this connection using [`Connection#model()`](/docs/api/connection.html#connection_Connection-model).
+ *
+ * ####Example
+ *
+ *     const conn = mongoose.createConnection();
+ *     const Test = conn.model('Test', mongoose.Schema({ name: String }));
+ *
+ *     Object.keys(conn.models).length; // 1
+ *     conn.models.Test === Test; // true
+ *
+ * @property models
+ * @memberOf Connection
+ * @instance
+ * @api public
+ */
+
+Connection.prototype.models;
+
 /**
  * The plugins that will be applied to all models created on this connection.
  *