[doc] Automate examples doc creation

The example READMEs currently have to be created with the bin/merge_cpp_and_md.sh script AFAIK. To execute the script you need to correct files and the correct file order. However I couldn't find the specific command for each example being documented anywhere.

Maybe we could create something like a .doc_config that lists this information for each example?

Then it would be also easy to create a script that builds all examples docs