docs(readme): add usage to the README

Add the detailed Usage section to the README.md file

Signed-off-by: Niloy Sikdar <[email protected]>

README.md

@@ -3,7 +3,9 @@
 ### Supercharge your .env using `neoenv` with more advanced controls and powers ☄️🚀
 
 Neoenv is a lightweight, zero-dependency, new-generation module for hassle-free, clean, typed and safe environment variables management for modern developers. 🔐🔥
-It loads environment variables from a `.env` file into [`process.env`](https://nodejs.org/docs/latest/api/process.html#process_process_env) and automatically generates configuration object based on the keys. 🤯
+It loads environment variables from a `.env` file into [`process.env`](https://nodejs.org/docs/latest/api/process.html#process_process_env) and automatically generates a configuration object based on the keys with a single command. 🤯
+Now, you'll be able to access the environment variables based on your `.env` file in a type-safe way with some nice IntelliSense and autocomplete. 🤩
+And guess what? It supports both JavaScript and TypeScript. 🎉
 
 Find the npm package [here](https://www.npmjs.com/package/neoenv)
 
@@ -22,7 +24,7 @@ First, let us discuss the problem which we're currently having. 🤔
 
 We use environment variables to store sensitive information like API keys, secrets, etc. which we don't want to commit to the repository. 🤫 That's why we use a `.env` file to store these variables and load them into `process.env`. Generally, we use the [`dotenv`](https://www.npmjs.com/package/dotenv) package to load the environment variables from the `.env` file. 📦 And we use the `process.env` object to access the variables.
 
-> `📝` A big thanks to [motdotla](https://github.com/motdotla) for creating [dotenv](https://github.com/motdotla/dotenv)
+> `📝` A big thanks to [motdotla](https://github.com/motdotla) for creating [dotenv](https://www.npmjs.com/package/dotenv)
 
 **Now that's all good for a general use case. But there are some problems with this approach!**
 
@@ -99,6 +101,86 @@ npm install --save neoenv
 yarn add neoenv
 ```
 
+## Usage
+
+If you've installed `neoenv` globally, you can use the `neoenv` command directly from the root of any project to generate the js/ts configuration file from the `.env` file. But you still need to install `neoenv` as a dependency in your project.
+
+So, the recommended way is to install `neoenv` as a dependency and use the `neoenv` command from the `package.json` scripts.
+
+After installing `neoenv` as a dependency, add a script to your `package.json` file to generate the config file using the `neoenv` command.
+
+```json
+{
+  "scripts": {
+    "gen:env": "neoenv --ts"
+  }
+}
+```
+
+This will generate an `env.config.ts` file in the root of your project. You can also use the `--js` flag to generate an `env.config.js` file.
+
+```json
+{
+  "scripts": {
+    "gen:env": "neoenv --js"
+  }
+}
+```
+
+Neoenv follows `Singleton Design Pattern`. Now, you can import the `envConfig` object from the generated file and use it to access the environment variables across your whole application in a type-safe way with some nice IntelliSense and autocomplete. 🤩
+
+Your generated file (`env.config.ts`) will look something like this (depending on the keys you have in your `.env` file):
+
+```ts
+import { register } from 'neoenv';
+register();
+
+export const envConfig = {
+  MONGODB_URI: process.env.MONGODB_URI as string,
+  GITHUB_CLIENT_ID: process.env.GITHUB_CLIENT_ID as string,
+  CLOUDINARY_API_KEY: process.env.CLOUDINARY_API_KEY as string,
+  JWT_SECRET: process.env.JWT_SECRET as string,
+};
+```
+
+Neoenv will handle everything from loading the environment variables from the `.env` file to generating the configuration object based on the keys available in the `.env` file automatically so that you don't have to do anything manually with copy-paste and you can safely focus on building your application. 🚀
+
+_You can also add the command to your `pre` hook (`prestart` for `start`, `predev` for `dev`) to generate the config file automatically before running your application after doing some changes in the `.env` file._
+
+```json
+{
+  "scripts": {
+    "prestart": "neoenv --js",
+    "start": "node index.js"
+  }
+}
+```
+
+or
+
+```json
+{
+  "scripts": {
+    "prestart": "yarn gen:env",
+    "start": "node index.js",
+    "gen:env": "neoenv --js"
+  }
+}
+```
+
+or
+
+```json
+{
+  "scripts": {
+    "predev": "neoenv --js",
+    "dev": "nodemon index.js"
+  }
+}
+```
+
+> **Note:** If you're using [nodemon](https://www.npmjs.com/package/nodemon) to run your application in development mode or using normal `node` (ex: `node index.js` or `node server.js`) with `start` command, you need to stop and restart the server after doing some changes in the `.env` file so that neoenv can load those new changes and generate the updated config file automatically.
+
 ## Bugs and Features
 
 See the [issues](https://github.com/niloysikdar/neoenv/issues) for a list of proposed features (and known issues). Feel free to raise new issues.
@@ -109,7 +191,7 @@ Distributed under the Apache-2.0 License. See [LICENSE](https://github.com/niloy
 
 ## Author
 
-### Niloy Sikdar
+**Niloy Sikdar**
 
 - [[email protected]](mailto:[email protected])
 - [GitHub](https://github.com/niloysikdar)