tell users they can what IP range Hub webhooks can come from so they can filter

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@docker.com> (github: SvenDowideit)

Signed-off-by: Sven Dowideit <SvenDowideit@docker.com>

docs/sources/docker-hub/builds.md

@@ -278,6 +278,10 @@ Webhooks are available under the Settings menu of each Repository.
 > **Note:** If you want to test your webhook out we recommend using
 > a tool like [requestb.in](http://requestb.in/).
 
+> **Note**: The Docker Hub servers are currently in the IP range
+> `162.242.195.64 - 162.242.195.127`, so you can restrict your webhooks to
+> accept webhook requests from that set of IP addresses.
+
 ### Webhook chains
 
 Webhook chains allow you to chain calls to multiple services. For example,

docs/sources/docker-hub/repos.md

@@ -105,9 +105,6 @@ Settings page. A webhook is called only after a successful `push` is
 made. The webhook calls are HTTP POST requests with a JSON payload
 similar to the example shown below.
 
-> **Note:** For testing, you can try an HTTP request tool like
-> [requestb.in](http://requestb.in/).
-
 *Example webhook JSON payload:*
 
 ```
@@ -141,6 +138,13 @@ new updates to your images and repositories. To get started adding webhooks,
 go to the desired repo in the Hub, and click "Webhooks" under the "Settings"
 box.
 
+> **Note:** For testing, you can try an HTTP request tool like
+> [requestb.in](http://requestb.in/).
+
+> **Note**: The Docker Hub servers are currently in the IP range
+> `162.242.195.64 - 162.242.195.127`, so you can restrict your webhooks to
+> accept webhook requests from that set of IP addresses.
+
 ### Webhook chains
 
 Webhook chains allow you to chain calls to multiple services. For example,