utf8: Update documentation

Addresses OfflineIMAP#498 (comment)

Signed-off-by: Urs Liska <git@ursliska.de>

offlineimap.conf

@@ -432,7 +432,7 @@ remoterepository = RemoteExample
 #proxy = SOCKS5:IP:9999
 
 
-# This option stands in the [Account Test] section.
+# EXPERIMENTAL: This option stands in the [Account Test] section.
 #
 # IMAP defines an encoding for non-ASCII ("international") characters, and most
 # IMAP servers store folder names in this encoding. Note that the IMAP 4rev1
@@ -446,22 +446,15 @@ remoterepository = RemoteExample
 #
 # WARNING: with this option enabled:
 # - compatibility with any other version is NOT GUARANTED (including newer);
+# - existing set-ups will probably break.
 # - no support is provided.
 #
-# This feature is EXPERIMENTAL and was merged because it's small changes in the
-# code.  However, this might seriously decrease the stability of the program.
-# That's why it will likely never be marked stable. The approach is: if it works
-# for you, you're lucky and you might choose to go for it. If it doesn't, sorry
-# but this feature is known to not work in many cases and it's not available to
-# you.  Enabling this feature might really be a poor choice for the future since
-# it's not supported at all and new releases might break the setup.
-#
 # IMPORTANT: READ THIS SECTION if you intend to enable this feature for an
-# EXISTING SYNCHRONIZATION pair!
-# Enabling UTF-8 encoded folder names will change many things on the local side
-# of a sync pair, so you really have to create a new local repository and review
-# the configuration. The least that would happen otherwise is a duplication of
-# all folders containing non-ASCII characters.
+# EXISTING ACCOUNT that has already been synchronized!
+# Enabling UTF-8 encoded folder names will change many things on the local
+# repository of an account, so you really have to create a new local repository
+# and review the configuration. The least that would happen otherwise is a
+# duplication of all folders containing non-ASCII characters.
 # But also the following functionality may change, so the configuration in the
 # remote repository configuration has to be reviewed/updated:
 # - decodefoldernames