docs: add a warning about public-api.ts exports for proxies

npm/ng-packs/packages/schematics/src/constants/proxy.ts

@@ -15,4 +15,8 @@ Finally, the name of the files and folders should not be changed for two reasons
 - Proxy generator will keep creating them at those paths and you will have multiple copies of the same content.
 - ABP Suite generates files which include imports from this folder.
 
+> **Important Notice:** If you are building a module and are planning to publish to npm,
+> some of the generated proxies are likely to be exported from public-api.ts file. In such a case,
+> please make sure you export files directly and not from barrel exports. In other words,
+> do not include index.ts exports in your public-api.ts exports.
 `;