docs: add missing version flag notes to intro.mdx

Author: sserrata

demo/docs/intro.mdx

@@ -371,6 +371,8 @@ yarn docusaurus gen-api-docs petstore --schemas-only
 
 > This command writes the schema pages to the configured output directory while leaving other generated docs untouched.
 
+The `--schemas-only` flag is also available for `gen-api-docs:version`.
+
 ### Cleaning API Docs
 
 To clean/remove all API Docs, run the following command from the root directory of your project:
@@ -397,6 +399,8 @@ To clean only schema docs while leaving API, info, and tag docs untouched, use t
 yarn docusaurus clean-api-docs petstore --schemas-only
 ```
 
+> The `--schemas-only` flag is also available for `clean-api-docs:version`.
+
 ### Versioning OpenAPI docs
 
 To generate _all_ versioned OpenAPI docs, run the following command from the root directory of your project: