Add new FAQ section "Why does my interface look weird?"

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

docs/content/faq.md

@@ -58,3 +58,22 @@ and make sure that `protocolUseSSL` / `CMD_PROTOCOL_USESSL` is set to `true` if
 ## HedgeDoc fails executing migrations and does not start
 Unfortunately, older versions of HedgeDoc had some bugs regarding migrations and didn't always record that a migration was executed.  
 Have a look at the *[Troubleshooting Migrations](/guides/migration-troubleshooting/)* guide for more information.
+
+## Why does my interface look weird?
+
+If your interface looks like this
+
+![Broken HedgeDoc interface](./faq/interface_broken.png)
+
+instead of this
+
+![Not broken HedgeDoc interface](./faq/interface_okay.png)
+
+then HedgeDoc can't find the asset files like images, stylesheets, fonts, etc.
+You should check the following settings (or their corresponding environment variables if you e.g. use docker.):
+
+- `domain` (env: `CMD_DOMAIN`)
+- `protocolUseSSL` (env: `CMD_PROTOCOL_USESSL`)
+- `urlAddPort` (env: `CMD_URL_ADDPORT`)
+
+Check [the reverse proxy guide](../guides/reverse-proxy/#configure-asset-link-generation) for an explanation.

docs/content/guides/reverse-proxy.md

@@ -12,7 +12,7 @@ This documentation will cover HTTPS setup, with comments for HTTP setup.
 
 ## HedgeDoc config
 
-[Full explanation of the configuration options](../configuration.md)
+### Useful configuration options
 
 | `config.json` parameter | Environment variable | Value | Example |
 |-------------------------|----------------------|-------|---------|
@@ -25,6 +25,23 @@ This documentation will cover HTTPS setup, with comments for HTTP setup.
 | `urlAddPort` | `CMD_URL_ADDPORT` | `false`, HedgeDoc should not append its port to the URLs it links | `false` |
 | `hsts.enable` | `CMD_HSTS_ENABLE` | `true` if you host over SSL, `false` otherwise | `true` |
 
+[Full explanation of the configuration options](../configuration.md)
+
+### Configure asset link generation
+
+HedgeDoc generates links to other pages and to assets (like images, stylesheets, fonts, etc) using the following settings. You must configure them according to the URL that you use to access your instance.
+
+- `domain` (env: `CMD_DOMAIN`)
+- `protocolUseSSL` (env: `CMD_PROTOCOL_USESSL`)
+- `urlAddPort` (env: `CMD_URL_ADDPORT`)
+
+!!! example
+    You access your HedgeDoc instance using a reverse proxy via `https://markdown.example`. You must set:
+
+    - `domain` to `markdown.example`.
+    - `protocolUseSSL` to `true` because you access your instance via HTTPS.
+    - `urlAddPort` to `false` because you access the instance using the default HTTPS port.
+
 
 ## Reverse Proxy config