Add documentation on environment variables

closes hagopj13#52

.env.example

@@ -1,7 +1,15 @@
+# Port number
 PORT=3000
+
+# URL of the Mongo DB
 MONGODB_URL=mongodb://127.0.0.1:27017/node-boilerplate
+
+# JWT
+# JWT secret key
 JWT_SECRET=thisisasamplesecret
+# Number of minutes after which an access token expires
 JWT_ACCESS_EXPIRATION_MINUTES=30
+# Number of days after which a refresh token expires
 JWT_REFRESH_EXPIRATION_DAYS=30
 
 # SMTP configuration options for the email service

README.md

@@ -11,7 +11,7 @@ By running a single command, you will get a production-ready Node.js app install
 
 ## Quick Start
 
-To create a Node.js project, simply run:
+To create a project, simply run:
 
 ```bash
 npx create-nodejs-express-app <project-name>
@@ -53,6 +53,7 @@ cp .env.example .env
 
 - [Features](#features)
 - [Commands](#commands)
+- [Environment Variables](#environment-variables)
 - [Project Structure](#project-structure)
 - [API Documentation](#api-documentation)
 - [Error Handling](#error-handling)
@@ -145,6 +146,34 @@ yarn prettier
 yarn prettier:fix
 ```
 
+## Enivornment Variables
+
+The environment variables can be found and modified in the `.env` file. They come with these default values:
+
+```bash
+# Port number
+PORT=3000
+
+# URL of the Mongo DB
+MONGODB_URL=mongodb://127.0.0.1:27017/node-boilerplate
+
+# JWT
+# JWT secret key
+JWT_SECRET=thisisasamplesecret
+# Number of minutes after which an access token expires
+JWT_ACCESS_EXPIRATION_MINUTES=30
+# Number of days after which a refresh token expires
+JWT_REFRESH_EXPIRATION_DAYS=30
+
+# SMTP configuration options for the email service
+# For testing, you can use a fake SMTP service like Ethereal: https://ethereal.email/create
+SMTP_HOST=email-server
+SMTP_PORT=587
+SMTP_USERNAME=email-server-username
+SMTP_PASSWORD=email-server-password
+EMAIL_FROM=support@yourapp.com
+```
+
 ## Project Structure
 
 ```