Install: log Rosetta detection, improve related docs

lib/libvips.js

@@ -115,6 +115,7 @@ const useGlobalLibvips = function () {
   }
   /* istanbul ignore next */
   if (isRosetta()) {
+    log('Detected Rosetta, skipping search for globally-installed libvips');
     return false;
   }
   const globalVipsVersion = globalLibvipsVersion();