How to set custom link on custom header?

I’m using WordPress custom header support to enable custom header upload via the back-end customization. I currently have the header href set to: <?php bloginfo(‘url’); ?> which successfully links my header to my main blog URL. But what I would like to do is this:

1) Create an option in the back-end under appearance > header, to enter a custom URL for the header image to link to.

2) Have a php code I can enter into my header.php (replacing the current bloginfo url php code) that will insert the link I’ve entered in the back-end, making the header link to the custom URL instead of the default bloginfo url.

I’ve searched the internet for guides but either there aren’t any or I just don’t know what exactly to search for, so now I’m here looking for help. I’m a PHP noob and have just started scratching the surface. A step by step guide for what I am trying to achieve would be much appreciated, and I’m sure there are others looking for the same solution.

Could someone with greater php and custom theme options knowledge please explain to me how this can be achieved? Your help will be much appreciated!