Added a Readme explaning a bit about JDK Packaging, which I just found in my working dir, which got lost a long time ago.

nbi/stub/ext/infra/build/products/jdk/README

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+In case you are wondering:
+The JDK is packaged for all platforms, only on OS it has to be a special installer item instead of a "bundled JDK", which works on all other platforms. This is (was?) a quirk in the NBI installer. 
+
+See #150