Add page for WASM example in ReactNative context

[riverKanies]

dario confirmed that they are already using bdk-wasm in reactNative
I think it would be very much worth including this as an example in the book, especially if it's the only option for RN. I think the bdk-wasm lib actually makes the most sense in a RN context as I personally wouldn't want to expose my keys to a browser. RN does give an extra layer of protection

[riverKanies]

@TristanBietsch want's to using bdk-wasm in a reactnative app, I'm going to help him do that and potentially make an open source starter example from that which we could link to form the "3rd party support" page