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/gl.po

@@ -6,7 +6,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: shadow 4.0.18\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: 2006-07-18 23:27+0200\n"
 "Last-Translator: Jacobo Tarrio <jtarrio@debian.org>\n"
 "Language-Team: Galician <trasno@ceu.fi.udc.es>\n"
@@ -516,7 +516,7 @@ msgid "%s: failed to drop privileges (%s)\n"
 msgstr "%s: non se puido deixar os privilexios (%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: teléfono da casa non válido: \"%s\"\n"
 
 #, fuzzy, c-format