Update macOS info on cgit about page

[Ryan Schmidt]

Hello,

I'd like to request a change to the following page:

https://git.zx2c4.com/cgit/about/

At the bottom it has a link for "OS X" with a link to a page on trac.macports.org. That's a link to the old MacPorts Subversion repository; we converted to Git in 2016. Also we now have a new web site with more user-friendly information for each port, rather than just the source code of the portfile, so it would be better to link to that:

https://ports.macports.org/port/cgit

And Apple changed the name of the operating system a few years ago, so the text of the link should be "macOS" not "OS X".

Thanks,
-Ryan, MacPorts