Update resize_vm_disk.md - add info how to see new disk size without reboot

admin-guide/configuration/resize_vm_disk.md

@@ -27,6 +27,12 @@ sda                      8:0    0   42G  0 disk
   └─vg_root-lv_home    253:5    0    2G  0 lvm  /home
 ```
 
+The command will probably not show the correct disk size. For this the VM either needs to be rebooted or you can trigger a re-read of the disksize without a reboot with this command (replace `sda` with the correct diskname you resized):
+```
+echo 1 > /sys/block/sda/device/rescan
+```
+
+
 Extend partition:
 ```bash
 [root@awi-ci-01 ~]# parted /dev/sda