[3.10] bpo-41963: document that ConfigParser strips off comments (GH-26197) (GH-26214)

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Laura Gutierrez Funderburk <58710704+lgfunderburk@users.noreply.github.com>
Co-authored-by: Jürgen Gmach <juergen.gmach@googlemail.com>

(cherry picked from commit 02ee8191263848f8c8999f72286148946b83e5c9)
diff --git a/Doc/library/configparser.rst b/Doc/library/configparser.rst
index 646e8a3..b0c2a2c 100644
--- a/Doc/library/configparser.rst
+++ b/Doc/library/configparser.rst
@@ -1153,6 +1153,13 @@
       *space_around_delimiters* is true, delimiters between
       keys and values are surrounded by spaces.
 
+   .. note::
+
+      Comments in the original configuration file are not preserved when
+      writing the configuration back.
+      What is considered a comment, depends on the given values for
+      *comment_prefix* and *inline_comment_prefix*.
+
 
    .. method:: remove_option(section, option)