Update docs on usage of external types in defineProps (#2600)

* Update composition-api.md

Add documentation for when types for `defineProps` are coming from an external file

* Update composition-api.md

* Update composition-api.md

src/guide/typescript/composition-api.md

@@ -50,6 +50,16 @@ const props = defineProps<Props>()
 </script>
 ```
 
+This also works if `Props` is imported from an external source. This feature requires TypeScript to be a peer dependency of Vue.
+
+```vue
+<script setup lang="ts">
+import type { Props } from './foo'
+
+const props = defineProps<Props>()
+</script>
+```
+
 #### Syntax Limitations {#syntax-limitations}
 
 In version 3.2 and below, the generic type parameter for `defineProps()` were limited to a type literal or a reference to a local interface.