Log on to Pure and click on the button 'Edit profile' in the middle of the page under your name and department. Click 'Edit' next to the section of text you want to add a hyperlink to. Highlight the content that you want to link from and click on the hyperlink (chain) icon. A new window will open in which you can copy in the URL. Click on 'Insert', then 'Update' and finally 'Save'.
Please see Pure support pages on editing profile text for more information.