Add SNAT docs, add Nginx docs

docs/firststeps-snat.md

@@ -0,0 +1,20 @@
+## SNAT
+
+SNAT is used to change the source address of the packets sent by mailcow.
+It can be used to change the outgoing IP on systems with multiple IP addresses.
+
+Open `mailcow.conf`, set either or both of the following parameters:
+
+```
+# Use this IPv4 for outgoing connections (SNAT)
+SNAT_TO_SOURCE=1.2.3.4
+
+# Use this IPv6 for outgoing connections (SNAT)
+SNAT6_TO_SOURCE=dead:beef
+```
+
+Run `docker-compose up -d`.
+
+The values are read by netfilter-mailcow. netfilter-mailcow will make sure, the post-routing rules are on position 1 in the netfilter table. It does automatically delete and re-create them if they are found on another position than 1.
+
+Check the output of `docker-compose logs --tail=200 netfilter-mailcow` to ensure the SNAT settings have been applied.

docs/u_e-nginx.md

@@ -0,0 +1,26 @@
+## Custom sites
+
+To create persistent (over updates) sites hosted by mailcow: dockerized, a new site configuration must be placed inside `data/conf/nginx/`:
+
+```
+nano data/conf/nginx/my_custom_site.conf
+```
+
+The filename is not important, as long as the filename carries a .conf extension.
+
+It is also possible to extend the configuration of the default file `site.conf` file:
+
+```
+nano data/conf/nginx/site.my_content.custom
+```
+
+This filename does not need to have a ".conf" extension, but follows the pattern `site.*.custom`, where `*` is a custom name.
+
+If PHP is to be included in a custom site, please use the PHP-FPM listener on phpfpm:9002 or create a new listener in `data/conf/phpfpm/php-fpm.d/pools.conf`.
+
+Restart Nginx (and PHP-FPM, if a new listener was created):
+
+```
+docker-compose restart nginx-mailcow
+docker-compose restart php-fpm-mailcow
+```

mkdocs.yml

@@ -28,6 +28,7 @@ pages:
   - 'SSL': 'firststeps-ssl.md'
   - 'Rspamd Web UI': 'firststeps-rspamd_ui.md'
   - 'Reverse Proxy': 'firststeps-rp.md'
+  - 'SNAT': 'firststeps-snat.md'
   - 'Setup a relayhost': 'firststeps-relayhost.md'
   - 'Logging': 'firststeps-logging.md'
   - 'Local MTA on Docker host': 'firststeps-local_mta.md'
@@ -62,6 +63,7 @@ pages:
       - "Expunge a User's Mails": 'u_e-dovecot-expunge.md'
       - 'More Examples with DOVEADM': 'u_e-dovecot-more.md'
       - 'Move vmail volume': 'u_e-dovecot-vmail-volume.md' 
+  - 'Nginx': 'u_e-nginx.md'
   - 'Redis': 'u_e-redis.md'
   - 'Rspamd': 'u_e-rspamd.md'
   - 'SOGo': 'u_e-sogo.md'