Update CODINGSTYLE.md

Co-authored-by: Egbert Rijke <[email protected]>

CODINGSTYLE.md

@@ -128,9 +128,8 @@ strategic endeavour to ensure the longevity, vitality, and success of the
     a = construction-of-a
   ```
 
-- **Lambda expressions**: We always wrap lambda expressions in parentheses, even
-  if it is the last argument of a function and thus isn't strictly required to
-  be parenthesized.
+- **Lambda expressions**: When a lambda expression appears as the argument of a function, we always wrap it in parentheses. We do this even if it is the last argument of a function, and thus isn't strictly required to
+  be parenthesized. Note that in some rare cases, a lambda expression might appear at the top level. In this case we don't require the lambda expression to be parenthesized.
 
   There are multiple syntaxes for writing lambda expressions in Agda. Generally,
   you have the following options: