offlineimap.conf: add more comments about decodefoldernames

Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap.conf

@@ -926,6 +926,14 @@ remoteuser = username
 # - compatibility with any other version is NOT GUARANTED (including newer);
 # - no support is provided.
 #
+# This feature 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.
+#
 #decodefoldernames = no