You can add a custom button to the main navigation bar, next to the logo. This button can lead to any URL of your choice.
To add the button:
<a href>
tag. <a target="_blank" href="https://en.wikipedia.org"><div style="width:30px;height:30px; background-size: 30px 30px; background-image:url(https://upload.wikimedia.org/wikipedia/en/8/80/Wikipedia-logo-v2.svg)" ></div></a> |