DOCS: Fixed small errors in the text and made code format more consistent

[xtophs]

Why are these changes needed?

Fix minor issues in docs:

• probably editing left over
• typo
• code formatting inconsistency

Related issue number

N/A

Checks

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