Docs: nginx reverse proxy, accessible via https

Thanks @leshacat

docs/nginx-reverse-proxy.md

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+Instructions for nginx reverse proxy, accessible via https (thanks [@leshacat](https://github.com/leshacat))
+
+* `sudo apt -y install nginx-full python-certbot-nginx`
+* Edit `/etc/nginx/sites-available/default`
+
+Leave the default config, scroll to the bottom, paste in at bottom and edit:
+```
+upstream explorer-servers {
+	ip_hash;
+	server srv1.example.com:3000 max_fails=1 weight=4;	
+	server srv2.example.com:3000 max_fails=1 weight=2;
+	server srv3.example.com:3000 max_fails=1 weight=1;		
+}
+
+server {
+	server_name explorer.example.com; # managed by Certbot
+	
+	proxy_set_header Host $host;
+	proxy_set_header X-Real-IP $remote_addr;
+	proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+	proxy_set_header X-Forwarded-Proto $scheme;
+	proxy_set_header X-Forwarded-Ssl on;
+
+	location / {
+
+		proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+		proxy_set_header Host $host;
+
+		proxy_pass http://explorer-servers;
+
+		proxy_http_version 1.1;
+		proxy_set_header Upgrade $http_upgrade;
+		proxy_set_header Connection "upgrade";
+
+		listen 80 default_server;
+		listen [::]:80 default_server;
+
+	}
+```
+
+* `systemctl enable nginx`
+*  `systemctl restart nginx`
+* `certbot --nginx -d explorer.example.com`