Add documentation examples for consider-using-in. (#6635)

Co-authored-by: Pierre Sassoulas <[email protected]>

Author: mbyrnepr2

doc/data/messages/c/consider-using-in/bad.py

@@ -0,0 +1,2 @@
+def fruit_is_round(fruit):
+    return fruit == "apple" or fruit == "orange" or fruit == "melon"  # [consider-using-in]

doc/data/messages/c/consider-using-in/good.py

@@ -0,0 +1,2 @@
+def fruit_is_round(fruit):
+    return fruit in {"apple", "orange", "melon"}