Extend documentation about loading media files (#317)

Fixes #312

docs/report/media.md

@@ -0,0 +1,41 @@
+---
+title: Using media files
+---
+
+## Images
+
+To load images into the reports/labels the report helper must be loaded in the template. 
+
+```html
+{% raw %}
+<!-- Load the report helper functions -->
+{% load report %}
+{% endraw %}
+```
+
+### Assets
+
+You can add images to the reports and labels by using the asset template tag:
+
+```html
+{% raw %}
+<!-- Load the report helper functions -->
+{% load report %}
+<img src="{% asset 'my_awesome_logo.png' %}"/>
+{% endraw %}
+```
+
+!!! info "Assets location"
+    You need to place your asset images to the report/assets directory in the [data directory](../start/docker_dev.md/#data-directory)
+
+### Part images
+
+You can render the images of the parts using the part_image template tag:
+
+```html
+{% raw %}
+<!-- Load the report helper functions -->
+{% load report %}
+<img src='{% part_image part %}'/>
+{% endraw %}
+```