[doc] Add an example for suppressed-message (#8328)

I initially wanted to activate invalid-name so we follow pep8 in our examples
but there's more than 50 violations right now. I much prefer to keep all of 
these weird issues contained to one documentation example rather than affecting
all other tests for it.

Co-authored-by: Daniel van Noord <13665637+DanielNoord@users.noreply.github.com>

Author: Pierre-Sassoulas

doc/data/messages/s/suppressed-message/bad.py

@@ -0,0 +1,9 @@
+### This is a contrived example, to show how suppressed-message works.
+### First we enable all messages
+# pylint: enable=all
+
+### Here we disable two messages so we get two warnings
+# pylint: disable=locally-disabled, useless-suppression # [suppressed-message, suppressed-message]
+
+### Here we disable a message, so we get a warning for suppressed-message again.
+"A"  # pylint: disable=pointless-statement # [suppressed-message, suppressed-message]

doc/data/messages/s/suppressed-message/details.rst

@@ -1 +1,4 @@
-You can help us make the doc better `by contributing <https://github.com/PyCQA/pylint/issues/5953>`_ !
+``suppressed-message`` is simply a way to see messages that would be raised
+without the disable in your codebase. It should not be activated most
+of the time. See also ``useless-suppression`` if you want to see the message
+that are disabled for no reasons.

doc/data/messages/s/suppressed-message/good.py

@@ -1 +1 @@
-# This is a placeholder for correct code for this message.
+"""Instead of a single string somewhere in the file, write a module docstring!"""