docs(config): add allowedHosts to dev-server docs (#1294)

Author: orteth01

Diff for: content/configuration/dev-server.md

@@ -6,6 +6,7 @@ contributors:
   - skipjack
   - spacek33z
   - charlespwd
+  - orteth01
 ---
 
 webpack-dev-server can be used to quickly develop an application. See the ["How to Develop?"](/guides/development) to get started.
@@ -46,6 +47,34 @@ W> Be aware that when [exporting multiple configurations](/configuration/configu
 T> If you're having trouble, navigating to the `/webpack-dev-server` route will show where files are served. For example, `http://localhost:9000/webpack-dev-server`.
 
 
+## `devServer.allowedHosts`
+
+`array`
+
+This option allows you to specify a whitelist of hosts that are allowed to access the dev server.
+
+```js
+allowedHosts: [
+    'host.com',
+    'subdomain.host.com',
+    'subdomain2.host.com',
+    'host2.com'
+]
+```
+
+Mimicking django's `ALLOWED_HOSTS`, a value beginning with `.` can be used as a subdomain wildcard. `.host.com` will match `host.com`, `www.host.com`, and any other subdomain of `host.com`.
+
+```js
+// this achieves the same effect as the first example
+// with the bonus of not having to update your config
+// if new subdomains need to access the dev server
+allowedHosts: [
+    '.host.com',
+    'host2.com'
+]
+```
+
+
 ## `devServer.clientLogLevel`
 
 `string`