Update github/microsoft/autogen link in chess documentation.

[kartikx]

Why are these changes needed?

An image in the Nested Chat Chess documentation is broken because it is linked to /microsoft/autogen.

Related issue number

Checks

• I've included any doc changes needed for https://ag2ai.github.io/ag2/. See https://ag2ai.github.io/ag2/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.

[kartikx]

Actually, I just noticed that all the links in this notebook are broken. It's because the source code specifies the links relatively,

See [nested chats tutorial chapter](/docs/tutorial/conversation-patterns#nested-chats)\n

Which is getting resolved to links like

[nested chats tutorial chapter](https://ag2ai.github.io/ag2/docs/docs/tutorial/conversation-patterns#nested-chats)

(Notice the double /docs)

Maybe this happened during the switchover to the new website?