TODO comments.

README.md

@@ -2568,3 +2568,31 @@ class Client {
 ```
 
 **[⬆ back to top](#table-of-contents)**
+
+### TODO comments
+
+When you find yourself that you need to leave notes in the code for some later improvements,
+do that using `// TODO` comments. Most IDE have special support for those kind of comments so that
+you can quickly go over the entire list of todos.  
+
+Keep in mind however that a *TODO* comment is not an excuse for bad code. 
+
+**Bad:**
+
+```ts
+function getActiveSubscriptions(): Promise<Subscription[]> {
+  // ensure `dueDate` is indexed.
+  return db.subscriptions.find({ dueDate: { $lte: new Date() } });
+}
+```
+
+**Good**
+
+```ts
+function getActiveSubscriptions(): Promise<Subscription[]> {
+  // TODO: ensure `dueDate` is indexed.
+  return db.subscriptions.find({ dueDate: { $lte: new Date() } });
+}
+```
+
+**[⬆ back to top](#table-of-contents)**