docs: update about options and templates

README.md

@@ -44,6 +44,13 @@ to_markdown(apiFile, outputFile, templates_dir, options)
 - If you want to use your own template, creates 'templates' directory and put [`api_doc_template.md.j2`](src/openapi_markdown/templates/api_doc_template.md.j2) file in it.
 - You can change templates directory by passing it as the 3rd argument of `to_markdown`.
 
+### Default templates
+
+There are internal templates you can use. If not set default is used.
+
+* templates - default
+* templates/embed - prints objects hierarchially as list in every request/response
+
 ## Development
 
 ### Requirements