[documentation] add ipv6 config for nginx (#367)

docs/installation_guide/nginx.md

@@ -59,6 +59,7 @@ The file you're about to create should look a bit like this:
 ```nginx.conf
 server {
   listen 80;
+  listen [::]:80;
   server_name example.com;
   location / {
     proxy_pass http://localhost:8080;
@@ -67,6 +68,8 @@ server {
 }
 ```
 
+Note: You can remove the line `listen [::]:80;` if your server is not ipv6 capable or you'd rather not use ipv6.
+
 Change `proxy_pass` to the ip and port that you're actually serving GoToSocial on and change `server_name` to your own domain name.
 If your domain name is `gotosocial.example.com` then `server_name gotosocial.example.com;` would be the correct value.
 If you're running GoToSocial on another machine with the local ip of 192.168.178.69 and on port 8080 then `proxy_pass http://192.168.178.69:8080;` would be the correct value.
@@ -86,7 +89,7 @@ sudo nginx -t
 
 If everything is fine you should get this as output:
 
-```
+```text
 nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
 nginx: configuration file /etc/nginx/nginx.conf test is successful
 ```