[tz] Proposed update to tz-link.htm for Microsoft Windows

Please find attached a patch which contains more specific information about time zone support in Microsoft Windows. In particular, I'm correcting the previous information which stated that the Windows time zone format was undocumented. I've provided links to all of the relevant documentation. I've also clarified the use of TZ data in the new Windows Runtime APIs. The previous text made it sound like DateTimeFormatter can perform CLDR conversions, which it cannot. Please let me know if there are any suggested revisions. Thanks, Matt