chore: update README.md to reflect type for import (#297)

src/modules/README.md

@@ -3,7 +3,7 @@
 A custom user module system. Place a `.ts` file with the following template, it will be installed automatically.
 
 ```ts
-import { UserModule } from '~/types'
+import type { UserModule } from '~/types'
 
 export const install: UserModule = ({ app, router, isClient }) => {
   // do something