docs: specify how nitrogen detect your specs (#14)

* docs: specify how nitrogen detect your specs

Just small addition that makes integration clearer

* chore: fix typo

packages/nitrogen/README.md

@@ -49,9 +49,10 @@ Every nitro module must have a `nitro.json` file at it's root level (i.e. the fo
 
 ### 3. Create a TypeScript spec
 
-The TypeScript spec is the single source of truth. It's interfaces, enums or other type declarations will be converted to C++ (or Swift/Kotlin) types using a code generator.
+The TypeScript spec is the single source of truth. It's interfaces, enums or other type declarations will be converted to C++ (or Swift/Kotlin) types using a code generator. Nitrogen will run on all `*.nitro.ts` files relative to your `nitro.json` config.
 
 ```ts
+// Image.nitro.ts
 export interface Image extends HybridObject<{ ios: 'c++', android: 'c++' }> {
   readonly width: number
   readonly height: number