[tz] Proposed patch - Theory change to reinstate reference to ISO-3166

[Stephen Colebourne]

Theory change to reinstate reference to ISO-3166

Use ISO-3166 as a guide for when a name should exist
Countries are not specified and nothing is mandated
--------------------------
https://github.com/jodastephen/tz/commit/e6199cc2616e938efb9422b263bd09da70220604

This patch reinstates the link to ISO-3166 in a softer way. In my
opinion, the original removal (of something present for 16 years) did
not have consensus and should have been reverted. However, I offer
this patch as a possible middle ground.

Stephen
--------------------------
@@ -316,6 +316,8 @@ in decreasing order of importance:
     'America/New_York' precludes 'America/New_York/Bronx'.
   Uninhabited regions like the North Pole and Bouvet Island
     do not need locations, since local time is not defined there.
+  Use ISO-3166 as a guide to ensuring time zone name coverage.
+    There should typically be at least one name per ISO-3166 code.
   If all the clocks in a region have agreed since 1970,
     don't bother to include more than one location
     even if subregions' clocks disagreed before 1970.