Fix typo found by Min ho Kim (#14879)

diff --git a/Lib/idlelib/help.py b/Lib/idlelib/help.py
index 652444a..e19d361 100644
--- a/Lib/idlelib/help.py
+++ b/Lib/idlelib/help.py
@@ -257,7 +257,7 @@
     same, help.html can be backported.  The internal Python version
     number is not displayed.  If maintenance idle.rst diverges from
     the master version, then instead of backporting help.html from
-    master, repeat the proceedure above to generate a maintenance
+    master, repeat the procedure above to generate a maintenance
     version.
     """
     src = join(abspath(dirname(dirname(dirname(__file__)))),