docs: Add documentation comment to scrub_list (#2769)

The new comment explains what the method does, allowing developers to more quickly understand the method's purpose.

Author: szokeasaurusrex

sentry_sdk/scrubber.py

@@ -67,6 +67,12 @@ def __init__(self, denylist=None, recursive=False):
 
     def scrub_list(self, lst):
         # type: (List[Any]) -> None
+        """
+        If a list is passed to this method, the method recursively searches the list and any
+        nested lists for any dictionaries. The method calls scrub_dict on all dictionaries
+        it finds.
+        If the parameter passed to this method is not a list, the method does nothing.
+        """
         if not isinstance(lst, list):
             return