Support RocksDB (#35)

Dockerfile

@@ -8,7 +8,8 @@ RUN VERSION=$(cat /tmp/VERSION) && \
     chmod a+x /usr/local/bin/* && \
     apk add --no-cache git build-base openssl && \
     apk add --no-cache --repository http://dl-cdn.alpinelinux.org/alpine/edge/community leveldb-dev && \
-    pip install aiohttp pylru plyvel websockets && \
+    apk add --no-cache --repository http://dl-cdn.alpinelinux.org/alpine/edge/testing rocksdb-dev && \
+    pip install aiohttp pylru plyvel websockets python-rocksdb && \
     git clone -b $VERSION https://github.com/kyuupichan/electrumx.git && \
     cd electrumx && \
     python setup.py install && \

README.md

@@ -25,6 +25,10 @@ If there's an SSL certificate/key (`electrumx.crt`/`electrumx.key`) in the `/dat
 
 You can view all ElectrumX environment variables here: https://github.com/kyuupichan/electrumx/blob/master/docs/environment.rst
 
+### RocksDB
+
+You can use RocksDB as the database engine instead of the default LevelDB by adding `-e DB_ENGINE=rocksdb` to your docker run. RocksDB should perform slightly better and use a little less disk space, but has to rebuild the databse.
+
 ### TCP Port
 
 By default only the SSL port is exposed. You can expose the unencrypted TCP port with `-p 50001:50001`, although this is strongly discouraged.