docs: add mongoose import to typescript example

When I first used the library I had no idea where "PaginateModel" was coming from and had to look in an issue from the library to find out. This change will make it clear that it's coming from mongoose.

Author: gabrielgasp

README.md

@@ -52,21 +52,22 @@ Prior to version `1.5.0`, types need to be installed from [DefinitelyTyped](http
 To declare a `PaginateModel` in your Typescript files:
 
 ```ts
+import mongoose from 'mongoose'
 import paginate from 'mongoose-paginate-v2';
 
 // declare your schema
-export const institutionSchema = new Schema({ name: String });
+export const institutionSchema = new mongoose.Schema({ name: String });
 
 // paginate with this plugin
 institutionSchema.plugin(paginate);
 
 // declare a mongoose document based on a Typescript interface representing your schema
-interface InstitutionDocument extends Document, InstitutionData {}
+interface InstitutionDocument extends mongoose.Document, InstitutionData {}
 
 // create the paginated model
 const model = mongoose.model<
   InstitutionDocument,
-  PaginateModel<InstitutionDocument>
+  mongoose.PaginateModel<InstitutionDocument>
 >('Institutions', institutionSchema, 'institutions');
 ```