Add getndf usage to the README

README.md

@@ -45,6 +45,43 @@ GOOS=windows GOARCH=386 CGO_ENABLED=0 go build -ldflags '-w -s' -o release/clien
 GOOS=darwin GOARCH=amd64 CGO_ENABLED=0 go build -ldflags '-w -s' -o release/client.darwin64 main.go
 ```
 
+To get an NDF from a network gateway and the permissioning server, use the `getndf` subcommand.  The `getndf` subcommand allows command line users to poll the NDF from both a gateway and the permissioning server without any pre-established client connection. It requires an IP address, port, and ssl certificate. You can download an ssl cert with:
+```
+openssl s_client -showcerts -connect permissioning.prod.cmix.rip:11420 < /dev/null 2>&1 | openssl x509 -outform PEM > certfile.pem
+```
+
+Example usage for Gateways:
+
+```
+$ go run main.go getndf --gwhost localhost:8440 --cert ~/integration/keys/cmix.rip.crt | jq . | head
+{
+  "Timestamp": "2021-01-29T01:19:49.227246827Z",
+  "Gateways": [
+    {
+      "Id": "BRM+Iotl6ujIGhjRddZMBdauapS7Z6jL0FJGq7IkUdYB",
+      "Address": ":8440",
+      "Tls_certificate": "-----BEGIN CERTIFICATE-----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\n6m52PyzMNV+2N21IPppKwA==\n-----END CERTIFICATE-----\n"
+    },
+    {
+      "Id": "JCBd9mAQb2BW8hc8H9avy1ubcjUAa7MHrPp0dBU/VqQB",
+```
+
+Example usage for the Permissioning server:
+
+```
+$ go run main.go getndf --permhost localhost:18000 --cert ~/integration/keys/cmix.rip.crt  | jq . | head
+{
+  "Timestamp": "2021-01-29T01:19:49.227246827Z",
+  "Gateways": [
+    {
+      "Id": "BRM+Iotl6ujIGhjRddZMBdauapS7Z6jL0FJGq7IkUdYB",
+      "Address": ":8440",
+      "Tls_certificate": "-----BEGIN CERTIFICATE-----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\n6m52PyzMNV+2N21IPppKwA==\n-----END CERTIFICATE-----\n"
+    },
+    {
+      "Id": "JCBd9mAQb2BW8hc8H9avy1ubcjUAa7MHrPp0dBU/VqQB",
+```
+
 Basic command line usage, sending unsafe, unencrypted messages to yourself:
 
 ```