docs(angular): add default content (#6844)

* docs(angular): add default content

* docs(angular): add space in default content

src/data/roadmaps/angular/content/default@h4MMn0_qUN3YXEdMUJOyd.md

@@ -1 +1,8 @@
-# @default
+# @default
+
+The `@default` clause is used to render a template when none of the `@case` blocks matches the value of the `@switch` conditional. `@default` is optional and can be omitted.
+
+Visit the following resources to learn more:
+
+- [@official@Angular Official Docs - @switch](https://angular.dev/guide/templates/control-flow#switch-block---selection)
+- [@article@Angular @switch: Complete Guide](https://blog.angular-university.io/angular-switch/)