feat: explain why nitro modules are needed as a dependency

Author: atlj

packages/create-react-native-library/templates/common/README.md

@@ -7,6 +7,8 @@
 <% if (project.nitro) { -%>
 ```sh
 npm install <%- project.slug %> react-native-nitro-modules
+
+> `react-native-nitro-modules` is required as this library relies on [Nitro Modules](https://nitro.margelo.com/).
 ```
 <% } else { -%>
 ```sh