document typical use cases

@xen-orchestra/mixins/docs/HttpProxy.md

@@ -4,6 +4,9 @@
 - [Usage](#usage)
   - [`xo-proxy`](#xo-proxy)
   - [`xo-server`](#xo-server)
+- [Use cases](#use-cases)
+  - [Access hosts in a private network](#access-hosts-in-a-private-network)
+  - [Allow upgrading xo-proxy via xo-server](#allow-upgrading-xo-proxy-via-xo-server)
 
 ## Set up
 
@@ -59,3 +62,13 @@ And use it in the URL:
 ```
 https://DiYBFavJwf9GODZqQJs23eAx9eh3KlsRhBi8RcoX0KM@xo.company.lan
 ```
+
+## Use cases
+
+### Access hosts in a private network
+
+To access hosts in a private network, deploy an XO Proxy in this network, expose its port 443 and use it as an HTTP proxy to connect to your servers in XO.
+
+### Allow upgrading xo-proxy via xo-server
+
+If your xo-proxy does not have direct Internet access, you can use xo-server as an HTTP proxy to make upgrades possible.