[3564] Extended the configuration example with the in-pool reservation.

One of the reservations is within the pool of dynamically allocated
addresses. The example demonstrates that the server will not allocate
this address dynamically and will only assign it to the client that
has a reservation for it.

doc/examples/kea4/reservations.json

@@ -29,7 +29,11 @@
 #  "rebind-timer": 2000,
 
 # Define a subnet with two reservations for the 192.0.2.202 and
-# 192.0.2.203 address.
+# 192.0.2.100 address. Note that the latter is a reservation for the
+# address which is within the range of the pool of the dynamically
+# allocated address. The server will exclude this address from this
+# pool and only assign it to the client which has a reservation for
+# it.
   "subnet4": [
     {
        "pools": [ { "pool":  "192.0.2.1 - 192.0.2.200" } ],
@@ -42,7 +46,7 @@
          },
          {
              "hw-address": "0a:0b:0c:0d:0e:0f",
-             "ip-address": "192.0.2.203"
+             "ip-address": "192.0.2.100"
          }
        ]
     }