Added cell-var-from-loop message example

Author: matusvalo

doc/data/messages/c/cell-var-from-loop/bad.py

@@ -0,0 +1,5 @@
+def foo(numbers):
+    for i in numbers:
+        def bar():
+            print(i)  # [cell-var-from-loop]
+        bar()

doc/data/messages/c/cell-var-from-loop/good.py

@@ -0,0 +1,7 @@
+def bar(x):
+    print(x)
+
+
+def foo(numbers):
+    for i in numbers:
+        bar(i)