Fix small typos in AutoGen 0.4 docs

[markdouthwaite]

Why are these changes needed?

Spotted two small typos while reviewing the in-progress 0.4 docs. Might be premature given the in-progress nature of 0.4, but thought I'd drop them in.

Keep up the great work!

Checks

• 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.

[rysweet]

Thanks Mark!

[markdouthwaite]

@microsoft-github-policy-service agree