Updated Debugging & FAQ (markdown)

Debugging-&-FAQ.md

@@ -7,10 +7,31 @@
 **Solution**  
 You did not properly insert a valid application key. Please [check here](https://github.com/invoiceninja/dockerfiles/wiki/prerequisites#generate-an-application-key) and the linked blog post.
 
-
 ## Debugging 
 Even when running your Invoice Ninja setup with Docker - errors can occur. Depending on where the error happens - the webserver, Invoice Ninja or the database - different log files can be responsible. 
 
+### Enable debug mode
+If you are not familiar with the command line or want to see error detail immediately on the screen instead of checking the logs, you can enable the _debug mode_ by setting `APP_DEBUG=true` as environment variable for the invoiceninja container.
+
+Your `docker-compose.yml` then might look like this:
+
+```yml
+services:
+  ...
+  app:
+    image: invoiceninja/invoiceninja:alpine-4
+    restart: always
+    environment: 
+      - APP_URL=https://invoiceninja.localhost
+      - APP_KEY=base64:123abc
+      - APP_DEBUG=true
+      ...
+    volumes:
+      ...
+```
+
+
+
 ### Show logs without `docker-compose`
 
 If you are not running `docker-compose` you first need to find the container id for your php container with `docker ps`. Then you can run