Added while-used message example (#6562)

Author: matusvalo

doc/data/messages/w/while-used/bad.py

@@ -0,0 +1,12 @@
+import requests
+
+
+def fetch_data():
+    i = 1
+    while i < 6:  # [while-used]
+        print(f'Attempt {i}...')
+        try:
+            return requests.get('https://example.com/data')
+        except requests.exceptions.RequestException:
+            pass
+        i += 1

doc/data/messages/w/while-used/good.py

@@ -0,0 +1,10 @@
+import requests
+
+
+def fetch_data():
+    for i in range(1, 6):
+        print(f'Attempt {i}...')
+        try:
+            return requests.get('https://example.com/data')
+        except requests.exceptions.RequestException:
+            pass

doc/data/messages/w/while-used/pylintrc

@@ -0,0 +1,2 @@
+[master]
+load-plugins=pylint.extensions.while_used

doc/data/messages/w/while-used/related.rst

@@ -0,0 +1 @@
+- `Stackoverflow discussion <https://stackoverflow.com/questions/920645/when-to-use-while-or-for-in-python>`_