Update transactions.md

docs/api/transactions.md

@@ -1,5 +1,23 @@
 # Transactions
 
-Transactions are currently an experimental feature as they can not be integrated as easily as the other Firebase features.
+Transactions are currently an experimental feature as they can not be integrated as easily as the other Firebase features. Please see the [Firebase documentation](https://firebase.google.com/docs/reference/js/firebase.database.Reference#transaction) for full implemtation details.
 
-TODO
+## Example
+
+```javascript
+const ref = firebase.database().ref('user/posts');
+
+ref.transaction((posts) => {
+  return (posts || 0) + 1;
+}, (error, committed, snapshot) => {
+  if (error) {
+    console.log('Something went wrong', error);
+  } else if (!committed) {
+    console.log('Aborted'); // Returning undefined will trigger this
+  } else {
+    console.log('User posts incremented by 1');
+  }
+  
+  console.log('User posts is now: ', snapshot.val());
+});
+```