[docs] Report helper docs (#12300)

* [docs] Report helper docs

* Split out docs for assets and snippets

* Updates

docs/docs/report/snippets.md

@@ -0,0 +1,52 @@
+---
+title: Report Snippets
+---
+
+## Report Snippets
+
+A powerful feature provided by the django / WeasyPrint templating framework is the ability to include external template files. This allows commonly used template features to be broken out into separate files and reused across multiple templates.
+
+To support this, InvenTree provides report "snippets" - short (or not so short) template files which cannot be rendered by themselves, but can be called from other templates.
+
+Snippet files are managed from the [Admin Center](../settings/admin.md#admin-center), via the *Report Snippets* panel. Staff users can upload new snippet files, and edit or remove existing snippets.
+
+Additionally, the content of an existing snippet can be modified directly within the browser - simply select a snippet from the table to open it in the built-in [template editor](./template_editor.md#editing-snippets).
+
+Snippets are included in a template as follows:
+
+```
+{% raw %}{% include 'snippets/<snippet_name.html>' %}{% endraw %}
+```
+
+For example, consider a custom stocktake report for a particular stock location, where we wish to render a table with a row for each item in that location.
+
+```html
+{% raw %}
+
+<table class='stock-table'>
+  <thead>
+    <!-- table header data -->
+  </thead>
+  <tbody>
+    {% for item in location.stock_items %}
+    {% include 'snippets/stock_row.html' with item=item %}
+    {% endfor %}
+  </tbody>
+
+{% endraw %}
+```
+
+!!! info "Snippet Arguments"
+    Note above that named argument variables can be passed through to the snippet!
+
+And the snippet file `stock_row.html` may be written as follows:
+
+```html
+{% raw %}
+<!-- stock_row snippet -->
+<tr>
+  <td>{{ item.part.full_name }}</td>
+  <td>{{ item.quantity }}</td>
+</tr>
+{% endraw %}
+```