add patching doc

docs/patching.md

@@ -2,6 +2,31 @@
 
 Patching a host manually could be time consuming (and boring). That's why we provide a high level feature downloading and applying all missing patches automatically.
 
-https://xen-orchestra.com/blog/hotfix-xs70e004-for-xenserver-7-0/
+## XOA smart patching system
+
+Your XOA will check for missing patching on official Citrix servers. They will be displayed if any:
+
+* in dashboard view
+* in pool view (plus the number of missing patches in a red pill)
+* in host view (in patching tab, same red pill)
+
+### Installing patches
+
+When you click on "Install all patches", XOA will automatically, at the same time (streaming all operations):
+
+* fetch all missing patches on Citrix servers
+* unzip them
+* upload them
+* apply them in correct order
+
+You can see more screenshots here: https://xen-orchestra.com/blog/hotfix-xs70e004-for-xenserver-7-0/
 
 > If you are behind a proxy, please update your `xo-server` configuration to add a proxy server, as [explained in the appropriate section](configuration.md#proxy-for-xenserver-updates-and-patches).
+
+## Notes on patching
+
+* Xen Orchestra won't reboot your hosts automatically. That's your call to choose when to do it.
+* Patching doesn't mean to reboot every time. Check the "Guidance" row: if "restartHost" is displayed, it means you need to reboot to have the patch fully apply (see screenshot below)
+* XO will install all patching without rebooting: that's not an issue. Even applying patches manually, **it's not mandatory to reboot after each patch**.
+
+![](./assets/xo5patching.png)