add blockchain cache

Dockerfile

@@ -125,6 +125,9 @@ ENV HOME /var/lib/steemd
 RUN useradd -s /bin/bash -m -d /var/lib/steemd steemd
 RUN chown steemd:steemd -R /var/lib/steemd
 
+# include blockchain seed in docker image to speed up startup
+ADD https://cdn.datavibe.net/f/eeqj/20160902.steemd-blockchain.tar.bz2 /var/cache/steemd/blockchain.tbz2
+
 VOLUME ["/var/lib/steemd"]
 
 # rpc service: