Added link to Japanese Translation

closes phpinternalsbook#6

Author: matthewtrask

README.md

@@ -32,6 +32,8 @@ These domains have been bought by Anthony to publish info about the book:
 
 Only the first domain is currently in use.
 
+A Japanese translation is already published and lives at [http://phpinternalsbook-ja.com/](http://phpinternalsbook-ja.com/).
+
 Authors
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