tests: README: note that -d *must* be 777 for the deleg tests

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13259

scripts/zfs-tests.sh

@@ -333,7 +333,7 @@ OPTIONS:
 	-m          Enable kmemleak reporting (Linux only)
 	-n NFSFILE  Use the nfsfile to determine the NFS configuration
 	-I NUM      Number of iterations
-	-d DIR      Use DIR for files and loopback devices
+	-d DIR      Use world-writable DIR for files and loopback devices
 	-s SIZE     Use vdevs of SIZE (default: 4G)
 	-r RUNFILES Run tests in RUNFILES (default: ${DEFAULT_RUNFILES})
 	-t PATH     Run single test at PATH relative to test suite

tests/README.md

@@ -88,6 +88,7 @@ The following zfs-tests.sh options are supported:
 
     -d DIR      Create sparse files for vdevs in the DIR directory.  By
                 default these files are created under /var/tmp/.
+                This directory must be world-writable.
 
     -s SIZE     Use vdevs of SIZE (default: 4G)