How can I display a web page at the end of the installation?

You can use a <launchBrowser> action inside a <finalPageActionList>, as shown in the example below. You can control the text displayed using the <progressText> tag.

<finalPageActionList>
<launchBrowser url="http://example.com/congratulations/" progressText="Visit Example website."></launchBrowser>
</finalPageActionList>