Added example for assignment-from-none

Co-authored-by: Vladyslav Krylasov <vladyslav.krylasov@gmail.com>

Author: 2 people

doc/data/messages/a/assignment-from-none/bad.py

@@ -0,0 +1,5 @@
+def function():
+    return None
+
+
+f = function()  # [assignment-from-none]

doc/data/messages/a/assignment-from-none/good.py

@@ -0,0 +1,5 @@
+def function():
+    return None
+
+
+f = function() if function() else 1