add auth basic to nginx configuration

replaces #230
From http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_read_timeout, it says

> Defines a timeout for reading a response from the proxied server. The timeout is set only between two successive read operations, not for the transmission of the whole response. If the proxied server does not transmit anything within this time, the connection is closed.

So I guess it's for a while `docker pull`? I wouldn't know. Been too long.