Add back title

Since we stopped using gradio.Interface for gradio.Blocks, we lost
Interface's title property. Fake it by adding a heading in markdown

description.md

@@ -1,3 +1,5 @@
+# RoBERTa Explainability
+
 In this demo, we use the RoBERTa language model (optimized for masked language modelling and finetuned for sentiment analysis).
 The model predicts for a given sentences whether it expresses a positive, negative or neutral sentiment.
 But how does it arrive at its classification?  This is, surprisingly perhaps, very difficult to determine.