Document reverse proxy usage with SignalR

We should write a doc that has example reverse proxy configurations and common pitfalls that can occur.

One example is that SSE with nginx likely wont work by default because the request is buffered.
Nginx configuration can turn buffering off via `proxy_buffering off;` but you might only want to turn it off for SignalR specific requests via:
```
server {
location /hubroute {
proxy_buffering off;
}
}
```
Another way to fix that issue is to send `X-Accel-Buffering: no` with your Http requests, so we could mention how to do that also.

WebSockets is another option that can sometimes need configuration in your proxies.
`proxy_set_header Connection $http_connection;`