Updated nginx proxy fronting with NPM guide

Updated the 'nginx reverse-proxy fronting' documentation with a guide for Nginx Proxy Manager, as you can't use the pre-existing nginx matrix.conf

examples/reverse-proxies/nginx/README.md

@@ -15,3 +15,75 @@ Copy the [matrix.conf](matrix.conf) file to your nginx server's filesystem, modi
 This configuration **disables SSL certificate retrieval**, so you will **need to obtain SSL certificates manually** (e.g. by using [certbot](https://certbot.eff.org/)) and set the appropriate path in `matrix.conf`. In the example nginx configuration, a single certificate is used for all subdomains (`matrix.DOMAIN`, `element.DOMAIN`, etc.). For your setup, may wish to change this and use separate `server` blocks and separate certificate files for each host.
 
 Also note that your copy of the `matrix.conf` file has to be adapted to whatever services you are using. For example, remove `element.domain.com` from the `server_name` list if you don't use [Element](../../../docs/configuring-playbook-client-element.md) web client or add `dimension.domain.com` to it if you do use the [Dimension](../../../docs/configuring-playbook-dimension.md) integration manager.
+
+## Using Nginx Proxy Manager
+
+Similar to standard nginx, [Nginx Proxy Manager](https://nginxproxymanager.com/) provides nginx capabilities but inside a pre-built Docker container. With the ability for managing proxy hosts and automatic SSL certificates via a simple web interface.
+
+If Matrix federation is enabled, then you will need to make changes to [NPM's Docker configuration](https://nginxproxymanager.com/guide/#quick-setup). By default NPM has access to ports 443, 80 and 81, but you would also need to **provide access to the fedderation ports** `8448` and `8449`.
+
+
+### Creating proxy hosts in Nginx Proxy Manager
+
+Open the 'Proxy Hosts' page in the NPM web interface and select `Add Proxy Host`, the first being for matrix web traffic. Apply the proxys configuration like this:
+
+```md
+# Details
+# Matrix web proxy config
+Domain Names: matrix.DOMAIN
+Scheme: http
+Forward Hostname/IP: IP-ADDRESS-OF-YOUR-MATRIX
+Forward Port: 81
+
+# Custom locations
+# Add one custom location
+Define location: /
+Scheme: http
+Forward Hostname/IP: IP-ADDRESS-OF-YOUR-MATRIX
+Forward Port: 81
+Custom config:
+    proxy_set_header X-Forwarded-For $remote_addr;
+    proxy_set_header X-Forwarded-Proto $scheme;
+    proxy_set_header X-Real-IP $remote_addr;
+    client_max_body_size 50M;
+
+# SSL
+# Either 'Request a new certificate' or select an existing one
+SSL Certificate: matrix.DOMAIN or *.DOMAIN
+Force SSL: true
+HTTP/2 Support: true
+```
+
+Again, under the 'Proxy Hosts' page select `Add Proxy Host`, this time for your federation traffic. Apply the proxys configuration like this:
+
+```md
+# Details
+# Matrix Federation proxy config
+Domain Names: matrix.DOMAIN:8448
+Scheme: http
+Forward Hostname/IP: IP-ADDRESS-OF-YOUR-MATRIX
+Forward Port: 8449
+
+# Custom locations
+# Add one custom location
+Define location: /
+Scheme: http
+Forward Hostname/IP: IP-ADDRESS-OF-YOUR-MATRIX
+Forward Port: 8449
+Custom config:
+    proxy_set_header X-Forwarded-For $remote_addr;
+    proxy_set_header X-Forwarded-Proto $scheme;
+    client_max_body_size 50M;
+
+# SSL
+# Either 'Request a new certificate' or select an existing one
+SSL Certificate: matrix.DOMAIN or *.DOMAIN
+Force SSL: true
+HTTP/2 Support: true
+
+# Advanced
+# Allows NPM to listen on the federation port
+Custom Nginx Configuration: listen 8448 ssl http2;
+```
+
+Also note, NPM would need to be configured for whatever other services you are using. For example, you would need to create additional proxy hosts for `element.DOMAIN` or `jitsi.DOMAIN`, which would use the forwarding port `81`.