Update docstring query about quoting backtick variables

Author: hwalinga

pandas/core/frame.py

@@ -3008,7 +3008,8 @@ def query(self, expr, inplace=False, **kwargs):
         expr : string
             The query string to evaluate.  You can refer to variables
             in the environment by prefixing them with an '@' character like
-            ``@a + b``.
+            ``@a + b``. You can refer to column names with spaces by quoting
+            them in backticks like ```a a` + b``.
         inplace : bool
             Whether the query should modify the data in place or return
             a modified copy