Org admins have the ability to add a company message that displays to all users. Should you like, you can add a link to this message as well.
Here is an example of a company message with a link:
"To learn more about Autodesk click Here."
To add a link to the word "Here" you would change the text as such:
To learn more about Autodesk click <a href="http://www.autodesk.com">Here</a>.
The <a> is where the link starts and the </a> is where the link ends.
Everything between these two will work as a link.