Update man page description of zpool rewind

Update description of zpool import --rewind-to-checkpoint in man/man7/zpoolconcepts.7
to explain that rewinding automatically discards a checkpoint.

Signed-off-by: Adi Gollamudi <[email protected]>
Closes #12646

Author: Adi-Goll

man/man7/zpoolconcepts.7

@@ -469,6 +469,11 @@ then rewind it during import:
 .Dl # Nm zpool Cm export Ar pool
 .Dl # Nm zpool Cm import Fl -rewind-to-checkpoint Ar pool
 .Pp
+Note that rewinding to a checkpoint will
+.Sy permanently discard it . 
+Once the pool has been successfully imported with the above rewind command, 
+you cannot rewind to the same checkpoint. 
+.Pp
 To discard the checkpoint from a pool:
 .Dl # Nm zpool Cm checkpoint Fl d Ar pool
 .Pp