Add documentation examples for redundant-keyword-arg (#7064)

Co-authored-by: Vladyslav Krylasov <vladyslav.krylasov@gmail.com>
Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

Author: 3 people

doc/data/messages/r/redundant-keyword-arg/bad.py

@@ -0,0 +1,5 @@
+def square(x):
+    return x * x
+
+
+square(5, x=4)  # [redundant-keyword-arg]

doc/data/messages/r/redundant-keyword-arg/details.rst

@@ -1 +1,7 @@
-# This is a placeholder for correct code for this message.
+def square(x):
+    return x * x
+
+
+square(x=4)
+# or
+square(5)