docs: document when BrowserWindow and BrowserView can be used (#33696)

We already document such info for other APIs, like the 'screen' API in
https://github.com/electron/electron/blob/f711fe6b5701196e5d803c04aab44bc62b392f8e/docs/api/screen.md?plain=1#L7-L8

.
So we should do the same thing for these ones too.

Signed-off-by: Darshan Sen <raisinten@gmail.com>