Update README.md

Author: awesomelike

README.md

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+# Use case
+Once your Express application is deployed, it is important to get notified of any errors in real-time. While there are many advanced solutions for this task already, this utility middleware focuses on being minimalistic, easy setup and of course the cosy Telegram :). 
+
+# Setup
+1. Write to [BotFather](https://t.me/botfather), give it a command `/newbot`, answer the questions, and it will give you a secret token (we call this `botToken`).
+2. Create a channel, give it a username, and add the bot you have just created to this channel.
+3. Inside of your project directory, run `npm install --save express-notify-telegram`. Afterwards, run `npx express-notify-telegram`, this CLI will ask you `botToken` and channel's username you created in the previous step and give you the channel's `chatId`.
+4. Finally, in your application, add the following:
+```js
+  const express = require('express');
+  const telegramMiddleware = require('express-notify-telegram');
+  
+  const app = express();
+  
+  app.use(telegramMiddleware({
+     botToken: '<your botToken from above>', 
+     chatId: '<the chatId you got from the CLI>'
+  }));
+  
+  // One of your endpoints
+  app.get('/resource', (req, res) => {
+    try {
+      // Some code that throws error
+    } catch(e) {
+      // This will fire a notification, as it has an erroneous 500 statusCode.
+      res.status(500).json({ /* whatever */ }); 
+      
+      // If you want a custom error message in the notification, add the following:
+      req.errorMessage = 'My custom error message';
+    }
+  });
+
+```