Create a Ribbon Button for Shared Document in SharePoint 2010

1/ Create Empty Project SharePoint
2/ Add New Item/Empty Element
3/ Open Elements.xml and copy them into this file.

<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
<CustomAction Id="DemoHelloWorldButton" RegistrationId="101"
RegistrationType="List" Location="CommandUI.Ribbon" Sequence="5"
Title="Hello World">
<CommandUIExtension>
<CommandUIDefinitions>
<CommandUIDefinition Location="Ribbon.Documents.Manage.Controls._children">
<Button Id="Ribbon.Documents.New.Controls.DemoHelloWorldButton"
Alt="Hello World Ribbon Button" Sequence="10"
Command="Demo_HelloWorld"
Image32by32="/_layouts/images/ribbon/demobutton.png"
LabelText="Hello World Demo" TemplateAlias="o1"/>
</CommandUIDefinition>
</CommandUIDefinitions>
<CommandUIHandlers>
<CommandUIHandler Command="Demo_HelloWorld" CommandAction="javascript:alert('Hello World!');" />
</CommandUIHandlers>
</CommandUIExtension>
</CustomAction>
</Elements>

4/ Deploy