docs: show new .toJSON() capability (#151)

Author: marcoscaceres

README.md

@@ -44,6 +44,40 @@ Finally, stop watching the user's location.
 navigator.geolocation.clearWatch(watchId);
 ```
 
+### `GeolocationPosition` as JSON
+
+You can also easily treat `GeolocationPosition` objects as JSON:
+
+```JS
+async function sendPosition() {
+  try {
+    // Get the current position
+    const position = await new Promise((resolve, reject) => {
+      navigator.geolocation.getCurrentPosition(resolve, reject);
+    });
+
+    // .stringify() calls .toJSON() automatically
+    const body = JSON.stringify(position, null, 2);
+
+    // Prepare the fetch request options
+    const options = {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json'
+      },
+      body
+    };
+
+    // Send request
+    await fetch('https://example.com/api/positions', options);
+  } catch (error) {
+    console.error('Error getting or sending position data:', error);
+  }
+}
+
+sendPosition();
+```
+
 ### More examples
 
 The specification provides [examples](https://w3c.github.io/geolocation-api/#examples) covering different use case.