docs: add more use cases for adding attachments

use-cases/attachments.md

@@ -21,3 +21,60 @@ const msg = {
   ],
 };
 ```
+Reading and converting a local PDF file. 
+```js
+import fs from 'fs';
+
+fs.readFile(('Document.pdf'), (err, data) => {
+  if (err) {
+    // do something with the error
+  }
+  if (data) {
+    const msg = {
+      to: 'recipient@test.org',
+      from: 'sender@test.org',
+      subject: 'Attachment',
+      html: '<p>Here’s an attachment for you!</p>',
+      attachments: [
+        {
+          content: data.toString('base64'),
+          filename: 'some-attachment.pdf',
+          type: 'application/pdf',
+          disposition: 'attachment',
+          contentId: 'mytext',
+        },
+      ],
+    };
+  }
+});
+  ```
+
+  If you are using a PDF URL: 
+  ```js
+ import request from 'request';
+
+request(fileURl, { encoding: null }, (err, res, body) => {
+  if (err) { return err; }
+  if (body) {
+    const textBuffered = Buffer.from(body);
+
+    const msg = {
+      to: 'recipient@test.org',
+      from: 'sender@test.org',
+      subject: 'Attachment',
+      html: '<p>Here’s an attachment for you!</p>',
+      attachments: [
+        {
+          content: textBuffered.toString('base64'),
+          filename: 'some-attachment.pdf',
+          type: 'application/pdf',
+          disposition: 'attachment',
+          contentId: 'mytext',
+        },
+      ],
+    };
+    // send msg here
+  }
+});
+   ```
+