Add a use case. Fix the URL of settings API.

Design:-Node-settings.md

@@ -1,6 +1,6 @@
 /settings API returns only the following built-in fields by default.
 
-http://nodered.jp/docs/api/admin/methods/get/settings/
+http://nodered.org/docs/api/admin/methods/get/settings/
 
 A node can add their own settings to be output with the above settings API.
 
@@ -47,3 +47,43 @@ The node settings in settings.js are not shown in the following cases.
 * The setting is not defined in any node.
 * A node setting sets false to exportable.
 * A node is disabled.
+
+## Use Cases
+### Change node color
+Currently, node color is fixed in each node. Using node settings, user can change a node color as they like.
+
+1. Add settings object to registerType definition in nodes/core/io/21-httprequest.js as follows.
+```
+    RED.nodes.registerType("http request",HTTPRequest,{
+        credentials: {
+            user: {type:"text"},
+            password: {type: "password"}
+        },
+        settings: {
+            httpRequestColor: {
+                value: "rgb(231, 231, 174)",
+                exportable: true
+            }
+        }
+    });
+```
+
+2. Change registerType definition in nodes/core/io/21-httprequest.html as follows.
+```
+<script type="text/javascript">
+    var nodeColor = RED.settings.nodeSettings.httpRequestColor;
+    RED.nodes.registerType('http request',{
+        category: 'function',
+        color: nodeColor,
+        defaults: {
+            ...
+```
+
+3. Add httpRequestColor definition in settings.js
+```
+module.exports = {
+    httpRequestColor: "rgb(255, 0, 0)",
+    ...
+```
+
+You can see an http request node with red color by following the above three steps.