DOC: Add missing question mark in README (#22251)

santosh2702 · gfyoung · commit 3bcc2bb4e275 · 2018-08-08T21:38:37.000-07:00
diff --git a/README.md b/README.md
@@ -89,7 +89,7 @@
 
 
 
-## What is it
+## What is it?
 
 **pandas** is a Python package providing fast, flexible, and expressive data
 structures designed to make working with "relational" or "labeled" data both
