docs: keepalive auto setting

docs/README.md

@@ -520,7 +520,9 @@ services:
 > **Warning**
 > This feature is experimental.  The behavior may change (or the feature may be removed entirely) without warning in a future release, even if the release is not a new major version.  If you use this feature, or if you would like to use this feature but you require changes to it first, please [provide feedback in #2194](https://github.com/nginx-proxy/nginx-proxy/discussions/2194).  Once we have collected enough feedback we will promote this feature to officially supported.
 
-To enable HTTP keep-alive between `nginx-proxy` and a backend server, set the `com.github.nginx-proxy.nginx-proxy.keepalive` label on the server's container to the desired maximum number of idle connections. See the [nginx keepalive documentation](https://nginx.org/en/docs/http/ngx_http_upstream_module.html#keepalive) and the [Docker label documentation](https://docs.docker.com/config/labels-custom-metadata/) for details.
+To enable HTTP keep-alive between `nginx-proxy` and backend server(s), set the `com.github.nginx-proxy.nginx-proxy.keepalive` label on the server's container either to `auto` or to the desired maximum number of idle connections. The `auto` setting will dynamically set the maximum number of idle connections to twice the number of servers listed in the corresponding `upstream{}` block, [per nginx recommendation](https://www.nginx.com/blog/avoiding-top-10-nginx-configuration-mistakes/#no-keepalives).
+
+See the [nginx keepalive documentation](https://nginx.org/en/docs/http/ngx_http_upstream_module.html#keepalive) and the [Docker label documentation](https://docs.docker.com/config/labels-custom-metadata/) for details.
 
 ### Headers