Add documentation around how to have a cs or cpp project

[kikisaints]

trafficstars

Customer is looking for a generated C# project instead of a C++. We have a way to do this, but it is not documented and should be.

[kikisaints]

npx react-native windows --language cs or npx react-native windows --language c++

[chrisglein]

The arguments are documented here: https://microsoft.github.io/react-native-windows/docs/getting-started#install-the-windows-extension Do we need more?

[PrplHaz4]

The arguments are documented here: https://microsoft.github.io/react-native-windows/docs/getting-started#install-the-windows-extension Do we need more?

It might make sense to link back to native-code-language-choice in the same spot