add build demo doc

ng2-components/README.md

@@ -54,3 +54,38 @@
 You can browse all the components at the following address:
 
 http://devproducts.alfresco.com/
+
+### How to test a change to a generic component in its own demo
+
+Let's suppose that for some reason you have changed a component and you want to test this changes.
+The example is based on the ng2-alfresco-login component, but you can use the same steps for any component.
+
+
+1.  Move inside the component folder and link it.
+```sh
+
+cd ng2-alfresco-login
+npm link
+
+```
+
+2.  Build the component with the watcher enabled.
+```sh
+
+npm run build:w
+
+```
+
+3. Move inside the demo folder and link the component to the local node_modules folder.
+```sh
+
+cd demo
+npm link ng2-alfresco-login
+
+```
+
+4. Start the demo project.
+```sh
+
+npm run start
+```