That's easy, but you will need a little bit of Lua and HTML knowledge.
go to your servers addons folder and then to ulx\lua\ulx\modules\sh, once in the "sh" folder create a new text document and name it "links.lua"
then paste this code into it:
CATEGORY_NAME = "Links"
function ulx.addons(ply)
ply:SendLua([[gui.OpenURL("
http://yourcustomwebsite.com/")]])
end
local website = ulx.command( CATEGORY_NAME, "ulx addons", ulx.addons, "!addons" )
website:defaultAccess( ULib.ACCESS_ALL )
website:help( "Open a list of the servers addons." )
You will need to create a website with a list of the addons on your server, then just place in the url into this code.
Good luck bro.