Product Handbook: Broken links to referecnes in other files

[gunbra32]

There seem to be two ways of cross-referencing between different rst files. One that does work on github and another one that works for the html pages.
Refer to:
https://github.com/lddubeau/rst-on-github/blob/7369c0e79d4d4848ab6d126ff51568e478651ee2/README.rst

I choose the "works for plain html" option as you can see here (links in the scope section):
https://github.com/CAB-LAB/cablab-core/blob/master/doc/intro.rst