Add section on adding titles to documents

website/docs/usage/visualizers.jade

@@ -153,6 +153,24 @@ p
     |  #[+a("https://tympanus.net/codrops/css_reference/background/") valid background value]
     |  or shorthand — including gradients and even images!
 
++h(3, "ent-titles") Adding titles to documents
+
+p
+    |  Rendering several large documents on one page can easily become confusing.
+    |  To add a headline to each visualization, you can add a #[code title] to
+    |  its #[code user_data]. User data is never touched or modified by spaCy.
+
++code.
+    doc = nlp(u'This is a sentence about Google.')
+    doc.user_data['title'] = 'This is a title'
+    displacy.serve(doc, style='ent')
+
+p
+    |  This feature is espeically handy if you're using displaCy to compare
+    |  performance at different stages of a process, e.g. during training. Here
+    |  you could use the title for a brief description of the text example and
+    |  the number of iterations.
+
 +h(2, "render") Rendering visualizations
 
 p