[doc] Add example to bad strip call (#6093)

So it's easier to understand what strip does without reading the documentation

Author: Pierre-Sassoulas

doc/data/messages/b/bad-str-strip-call/bad.py

@@ -1,2 +1,4 @@
-my_string = "Hello World"
-my_string.strip("Hello")  # [bad-str-strip-call]
+"Hello World".strip("Hello")  # [bad-str-strip-call]
+# >>> ' World'
+"abcbc def bacabc".strip("abcbc ")  # [bad-str-strip-call]
+# >>> 'def'

doc/data/messages/b/bad-str-strip-call/good.py

@@ -1,2 +1,4 @@
-my_string = "Hello World"
-my_string.strip("Helo")
+"Hello World".strip("Helo")
+# >>> ' World'
+"abcbc def bacabc".strip("abc ")
+# >>> 'def'