docs: add more details to the doc

Add more details to the doc

Signed-off-by: Hage Yaapa <hage.yaapa@in.ibm.com>

README.md

@@ -20,6 +20,65 @@ npm i
 npm start
 ```
 
+The main app will be running at `http://[::1]:3000`.
+
+You will also see `Recommendation server is running at http://127.0.0.1:3001.`, it is the server to which
+the `services/recommender.service` service will connect to get the recommendations for a user.
+
+## Usage
+
+This app is intended to be interacted with using the API Explorer located at http://[::1]:3000/explorer/.
+
+## Models
+
+This app has five models:
+
+1. `User` - representing the users of the system
+2. `Product` - a model which is mapped to a remote service by `services/recommender.service`
+3. `ShoppingCartItem` - a model for representing purchases
+4. `ShoppingCart` - a model to represent a user's shopping cart, can contain many items (`item`) of the type `ShoppingCartItem`
+5. `Order` - a model to represent an order by user, can have many products (`products`) of the type `ShoppingCartItem`
+
+`ShoppingCart` and `Order` are marked as belonging to the `User` model by the use of the `@belongsTo` model decorator. Correspondingly, the `User` model is marked as having many `Order`s using the `@hasMany` model decorator. Although possible, a `hasMany` relation for `User` to `ShoppingCart` has not be created in this particular app to limit the scope of the example.
+
+## Controllers
+
+Controllers expose API endpoints for interacting with the models and more.
+
+In this app, there are four controllers:
+
+1. `ping` - a simple controller to checking the status of the app
+2. `user` - controller for creating user, fetching user info, updating user info, and logging in
+3. `shopping-cart` - controller for creating, updating, deleting shopping carts, and getting the details about a shopping cart
+4. `user-order` - controller for creating, updating, deleting orders, and getting the details about an order
+
+## Services
+
+Services are modular components that can be plugged into a LoopBack application in various locations to contribute
+additional capabilities and features to the application.
+
+This app has five services:
+
+1. `services/hash.password.bcryptjs` - responsible for generating and comparing password hashes.
+2. `services/jwt-service` - responsible for generating and verifying JSON Web Token.
+3. `services/recommender.service` - responsible for connecting to a "remote" server and getting recommendations for a user. The API endpoint at `GET /users​/{userId}​/recommend`, is made possible by this service.
+4. `services/user-service` - responsible for verifying if user exists and the submitted password matches that of the existing user.
+5. `services/validator` - responsible for validating email and password when a new user is created.
+
+## Login
+
+The endpoint for logging in a user is a `POST` request to `/users/login`.
+
+Once the credentials are extracted, the logging-in implementation at the controller level is just a four step process. This level of simplicity is made possible by the use of the `UserService` service provided by
+ `@loopback/authentication`.
+
+1. `const user = await this.userService.verifyCredentials(credentials)` - verify the credentials
+2. `const userProfile = this.userService.convertToUserProfile(user)` - generate user profile object
+3. `const token = await this.jwtService.generateToken(userProfile)` - generate JWT based on the user profile object
+4. `return {token}` - send the JWT
+
+You can see the details in `packages/shopping/src/controllers/user.controller.ts`.
+
 ## Contributing
 
 This project uses [DCO](https://developercertificate.org/). Be sure to sign off