The link was created automatticly, if you have a profile on wordpress.org.
As example: see my profile: http://profiles.wordpress.org/bueltge/
and see also a plugin of my, same user-slug: http://wordpress.org/plugins/adminimize/
But it is important, that you write case sensitive. The user must include in the readme of the plugin, on the string Contributors:. See also a example from the plugin above: http://plugins.svn.wordpress.org/adminimize/trunk/readme.txt
=== Adminimize ===
Contributors: Bueltge, inpsyde
....