Add new file

doc/api/lease4-update.json

+{
+    "name": "lease4-update",
+    "brief": "The lease4-update command can be used to update existing leases.",
+    "description": "See <xref linkend=\"lease4-update\"/>",
+    "support": [ "kea-dhcp4", "kea-dhcp6" ],
+    "avail": "1.3.0",
+    "hook": "lease_cmds",
+    "cmd-syntax": "{
+  \"command\": \"lease4-update\",
+  \"arguments\": {
+    \"ip-address\": \"192.0.2.1\",
+    \"hostname\": \"newhostname.example.org\",
+    \"hw-address\": \"1a:1b:1c:1d:1e:1f\",
+    \"subnet-id\": 44,
+    \"force-create\": true
+  }
+}",
+}
\ No newline at end of file