Merge pull request #293 from gvolpe/docs/components-graphic

Add components illustration

Author: gvolpe

README.md

@@ -7,9 +7,22 @@ shopping-cart
 
 ⚠️ **IMPORTANT NOTICE** If you come here from [Practical FP in Scala](https://leanpub.com/pfp-scala), go to the [master](https://github.com/gvolpe/pfps-shopping-cart/tree/master) branch. You're now on the `second-edition` branch, which is the new default, as I'm currently working on the 2nd edition of the book. ⚠️
 
+## Components Overview
+
+Here's an overview of the different components that make this application.
+
+[!components](./components.png)
+
+- Both **Services** and **Authentication** are *algebras*. The latter are mainly dependencies for some of the services.
+- Programs shows **Checkout**, the business logic that combines most of the services.
+- Effects show our custom interfaces required implicitly.
+- The lines connecting services to Redis and PostgreSQL show which ones access which storage.
+- The HTTP layer shows the client and the different routes.
+- At the very end, we have both the modules and the entry point to the application.
+
 ## Authentication Data
 
-For didactic purposes this information is made available to the readers but in a real application *THIS SHOULD NEVER BE MADE PUBLIC*.
+For didactic purposes, this is made available to the readers but in a real application *THIS SHOULD NEVER BE MADE PUBLIC*.
 
 For Admin users, the following environment variables are needed:
 
@@ -60,7 +73,6 @@ sbt test
 
 To run Integration Tests we need to run both `PostgreSQL` and `Redis`:
 
-
 ```
 docker-compose up
 sbt it:test