Sometimes, it pays to follow the paper trail, and, the documents filed by Pinterest Europe Ltd in recent days are of the memorable kind that the company could pin to its own board. Indeed, there are now converging indications that Pinterest is about to go truly global – and that, like other Silicon Valley social networks before it, it has chosen to do so out of Dublin. The documents reveal that the Dublin subsidiary of the San Francisco-based visual social media group received three separate cash injections totalling $139 million on July 13. Then on August 24, the company got…