schemas: document ManagedHost property usage

Since there were questions about this property, clarify the expected
values and what it can be used for [1].

References:
[1] https://gerrit.openbmc.org/c/openbmc/bmcweb/+/73855

Change-Id: I4add078b191879132754b9d30546634a6cc70fd7
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/schemas/openbmc-dbus.json b/schemas/openbmc-dbus.json
index 7f49810..05d4669 100644
--- a/schemas/openbmc-dbus.json
+++ b/schemas/openbmc-dbus.json
@@ -60,6 +60,7 @@
                             "type": "object"
                         },
                         "ManagedHost": {
+                            "description": "Used to enumerate hosts from 1 to N on multi-host platforms. Set to 0 for a single-host system. Can be used to map a host to e.g. a systemd service instance.",
                             "additionalProperties": false,
                             "properties": {
                                 "HostIndex": {