Issue #24894: Document the codec iso8859_11

Patch written by Prashant Tyagi.
diff --git a/Doc/library/codecs.rst b/Doc/library/codecs.rst
index f3017da..628969c 100644
--- a/Doc/library/codecs.rst
+++ b/Doc/library/codecs.rst
@@ -1130,6 +1130,8 @@
 +-----------------+--------------------------------+--------------------------------+
 | iso8859_10      | iso-8859-10, latin6, L6        | Nordic languages               |
 +-----------------+--------------------------------+--------------------------------+
+| iso8859_11      | iso-8859-11, thai              | Thai languages                 |
++-----------------+--------------------------------+--------------------------------+
 | iso8859_13      | iso-8859-13, latin7, L7        | Baltic languages               |
 +-----------------+--------------------------------+--------------------------------+
 | iso8859_14      | iso-8859-14, latin8, L8        | Celtic languages               |