[Docs] Fixed links in sitetypes.jl to the new site

[VinceNeede]

Description

In the last changes the links in sitetype.jl became again unreachable. I don't know if you were already scheduling to change them but since I noticed it I thought to change them on the fly, hoping you don't mind.

How Has This Been Tested?

The new links correctly send to the new site

Checklist:

• My code follows the style guidelines of this project. Please run using JuliaFormatter; format(".") in the base directory of the repository (~/.julia/dev/ITensors) to format your code according to our style guidelines.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that verify the behavior of the changes I made.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.

[mtfishman]

Good catch, thanks!