MAINT: Fix grammar in user_guide/scale.rst (pandas-dev#29848)

Follow-up to:

pandas-dev#29811

Author: gfyoung

doc/source/user_guide/scale.rst

@@ -94,7 +94,7 @@ Use efficient datatypes
 
 The default pandas data types are not the most memory efficient. This is
 especially true for text data columns with relatively few unique values (commonly
-referred to as "low-cardinality" data). By using more efficient data types you
+referred to as "low-cardinality" data). By using more efficient data types, you
 can store larger datasets in memory.
 
 .. ipython:: python