Update README.md for Sematic Router Example

[tarockey]

Added contributors to recognize the other devs who helped build the example

Why are these changes needed?

Quick update the add contributors to the Semantic_Router distributed agent example.

Related issue number

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.