Add documentation for live patching systemVMs (#267)

* Add documentation for live patching systemVMs

* add more details

* address comments
diff --git a/source/upgrading/upgrade/_sysvm_restart.rst b/source/upgrading/upgrade/_sysvm_restart.rst
index 8f01fb2..0376ce3 100644
--- a/source/upgrading/upgrade/_sysvm_restart.rst
+++ b/source/upgrading/upgrade/_sysvm_restart.rst
@@ -15,9 +15,48 @@
 
 .. sub-section included in upgrade notes.
 
-Once you've upgraded the packages on your management servers, you'll
+From Apache CloudStack version 4.17.0 onward, there is support to live patch 
+system VMs, namely, SSVM, CPVM, Routers. Live patching provides support 
+for zero-downtime upgrades, wherein, the System VM software is updated to the
+latest code version without having to destroy and recreate them / restart them.
+
+With this feature, users will have a choice wherein they can use the existing system VM template with the latest
+software by using the live patch feature, or can follow the usual workflow of restarting the
+system VM to use the latest system VM template. Live Patching system VMs serves to be especially
+useful in cases when the code version has upgraded but the template hasn't. In such a scenario users
+will no longer need to restart the system VMs to use the latest code.
+
+When one attempts to live-patch the system VMs, it pretty much mimics the patching process
+that happens when booting up the System VMs but with having to shut down the system VMs. 
+This will update the software packages, which were previously bundled in the systemvm.iso i.e., 
+agent.zip and cloud-scripts.tgz and restart the services that are present in the /var/cache/cloud/enabled_svcs file
+in the system VMs.
+
+.. note::
+
+   The following services will be restarted once a system VM is live patched:
+
+            +---------------------+-------------------------------+
+            | **System VM**       |         **Services**          |
+            +---------------------+-------------------------------+
+            | SSVM                | cloud, apache2, portmap       |
+            +---------------------+-------------------------------+
+            | CPVM                | cloud                         |
+            +---------------------+-------------------------------+
+            | VRs                 | haproxy, apache2, dnsmasq     |
+            +---------------------+-------------------------------+
+
+   With respect to VRs, a network restart without cleanup is initiated to during live patching to ensure all rules
+   are re-applied. 
+
+   **NOTE:** In case there is an absolute need to upgrade the system VM template due to availability of
+   security patches or update in a package provided by the template, then the old workflow of recreating the system
+   VM will need to be followed, which would mean noticible downtime.
+
+In addition to the support for live patching, users still have the facility to follow the legacy workflow
+of restarting the system VMs once the packages on the management servers have been upgraded. Here you'll
 need to restart the system VMs in order for those VMs to be rebuilt 
-from the new systemVM template version.
+from the new system VM template version.
 
 .. note::