Add kernel information to start-up

Author: simonkurtz-MSFT

.devcontainer/post-start-setup.sh

@@ -73,6 +73,8 @@ echo "        - Wait for all extensions to install"
 echo "        --> ✅ (.venv) prefix will appear when you open a new terminal"
 echo ""
 echo "   3. Start using the infrastructures and samples!"
+echo "        - You may initially need to select the kernel (top-right above the" 
+echo "          Jupyter notebook). If so, select the '.venv' Python environment."
 echo ""
 echo "============================================================================"
 echo -e "\n\n"