added doc comments to all formatters

html_to_django/formatters/var_formatter.py

@@ -1,9 +1,16 @@
 """
-Find tags with a "dj-var" attribute and replace its content with the
-value enclosed in {{ }}.
+var_formatter.py
+
+This module contains a function `format` that modifies a BeautifulSoup object in place.
+
+The `format` function searches for all elements with the attribute "dj-var". For each found element, it replaces the
+element's content with a Django template variable that has the same name as the value of the "dj-var" attribute.
+Then it removes the "dj-var" attribute from the element.
+
+Example:
+    If an element is <p dj-var="greeting">Hello, world!</p>,
+    after processing, it becomes <p>{{ greeting }}</p>.
 """
-
-
 from bs4 import BeautifulSoup