bitcoin.bib: Add Satoshi paper URL and date

Date according to Wikipedia which cites other source.

Author: jsarenik

doc/bitcoin.bib

@@ -16,7 +16,9 @@ @misc{Poon2015Lightning
 @misc{nakamoto2008bitcoin,
 	title={{Bitcoin: A peer-to-peer electronic cash system}},
 	author={Nakamoto, Satoshi},
-	year={2008}
+	note = {\url{https://bitcoin.org/bitcoin.pdf}},
+	year={2008},
+	urldate ={2008-10-31}
 }
 @misc{BitcoinChannels,
 	title =	{{Instant TX for established business relationships (need replacements/nLockTime)}},