help: Introduce separate section for external resources

The plan is to describe them all more carefully.
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/crtools.c

@@ -827,6 +827,15 @@ usage:
 "                        restore making it the parent of the restored process\n"
 "  --freeze-cgroup       use cgroup freezer to collect processes\n"
 "\n"
+"* External resources support:\n"
+"  --external RES        dump objects from this list as external resources:\n"
+"                        Formats of RES on dump:\n"
+"                            tty[rdev:dev]\n"
+"                            file[mnt_id:inode]\n"
+"                            dev[maj:min]:VAL\n"
+"                        Formats of RES on restore:\n"
+"                            dev[VAL]:DEVPATH\n"
+"\n"
 "* Special resources support:\n"
 "  -x|--" USK_EXT_PARAM " [inode,...]\n"
 "                        allow external unix connections (optional arguments\n"
@@ -879,13 +888,6 @@ usage:
 "  --enable-fs FSNAMES   a comma separated list of filesystem names or \"all\"\n"
 "                        force criu to (try to) dump/restore these filesystem's\n"
 "                        mountpoints even if fs is not supported\n"
-"  --external RES        dump objects from this list as external resources:\n"
-"                        Formats of RES on dump:\n"
-"                            tty[rdev:dev]\n"
-"                            file[mnt_id:inode]\n"
-"                            dev[maj:min]:VAL\n"
-"                        Formats of RES on restore:\n"
-"                            dev[VAL]:DEVPATH\n"
 "  --inherit-fd fd[NUM]:RES\n"
 "                        Inherit file descriptors, treating fd NUM as being\n"
 "                        already opened via an existing RES, which can be:\n"