libmisc/root_flag: add tips for --root flag only support abspath

- Add tips in error message.
- Add tips in man.
- Add zh_CN and zh_TW for tips.

Signed-off-by: Celeste Liu <coelacanthus@outlook.com>

po/it.po

@@ -25,7 +25,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: shadow 4.1.1\n"
 "Report-Msgid-Bugs-To: pkg-shadow-devel@lists.alioth.debian.org\n"
-"POT-Creation-Date: 2022-04-27 16:54+0200\n"
+"POT-Creation-Date: 2022-07-27 22:49+0800\n"
 "PO-Revision-Date: 2008-03-27 14:40+0100\n"
 "Last-Translator: Danilo Piazzalunga <danilopiazza@gmail.com>\n"
 "Language-Team: Italian <tp@lists.linux.it>\n"
@@ -538,7 +538,7 @@ msgid "%s: failed to drop privileges (%s)\n"
 msgstr "%s: impossibile abbandonare i privilegi (%s)\n"
 
 #, fuzzy, c-format
-msgid "%s: invalid chroot path '%s'\n"
+msgid "%s: invalid chroot path '%s', only absolute paths are supported.\n"
 msgstr "%s: telefono di casa «%s» non valido\n"
 
 #, fuzzy, c-format