Comment the HTMLPrintContext class.

diffoscope/presenters/html/html.py

@@ -386,6 +386,10 @@ class HTMLPrintContext(
         "target single_page jquery_url css_url our_css_url icon_url used_anchors",
     )
 ):
+    """
+    Hold states scoped to a single run of the HTMl generation.
+    """
+
     @property
     def directory(self):
         return None if self.single_page else self.target