Update instances_create.md

Added instructions on how to install the incus agent manually.

Signed-off-by: Simos Xenitellis <[email protected]>

doc/howto/instances_create.md

@@ -137,3 +137,20 @@ You should now see the installer. After the installation is done, you need to de
     incus storage volume detach <pool> iso-volume iso-vm
 
 Now the VM can be rebooted, and it will boot from disk.
+
+### Install the Incus Agent into virtual machine instances
+
+Incus requires an agent software to run in a virtual machine in order to control the instance in the same way as container instances. This agent software is the Incus Agent. The virtual machine images from the https://images.linuxcontainers.org/ remote have been configured so that they can transparently install and enable the Incus Agent software. 
+
+However, other virtual machine images may not have the functionality to automatically install and enable the Incus Agent. Therefore, you have to perform this task manually. 
+
+Incus provides the Incus Agent in a remote filesystem with mount name `config`. The type of the filesystem is `9p`.
+You first need to get access to the virtual machine and run the following commands. The first line will mount the remote filesystem on the mount point `/mnt`. The subsequent commands will run the installation script `install.sh` to install and run the Incus Agent. You need to perform this task once.
+
+    mount -t 9p config /mnt
+    cd /mnt
+    ./install.sh
+
+```{note}
+The Incus Agent is currently available only on Linux virtual machines.
+```