update notebook wording and format

Why are these changes needed?

Make the notebook format cleaner.

[ ] I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
[ ] I've added tests (if relevant) corresponding to the changes introduced in this PR.
[ ] I've made sure all auto checks have passed.