Added assignment-from-no-return message example (#5992)

Co-authored-by: Vladyslav Krylasov <vladyslav.krylasov@gmail.com>
Co-authored-by: Daniël van Noord <13665637+DanielNoord@users.noreply.github.com>

Author: 3 people

doc/data/messages/a/assignment-from-no-return/bad.py

@@ -0,0 +1,5 @@
+def add(x, y):
+    print(x + y)
+
+
+value = add(10, 10)  # [assignment-from-no-return]

doc/data/messages/a/assignment-from-no-return/good.py

@@ -0,0 +1,5 @@
+def add(x, y):
+    return x + y
+
+
+value = add(10, 10)