Merge pull request #4117 from cilphex/docker-readme-update

Fix text in docker readme

docker/README.md

@@ -23,7 +23,7 @@ environment for testing as one doesn't need to wait tens of minutes for blocks
 to arrive in order to test channel related functionality. Additionally, it's
 possible to spin up an arbitrary number of `lnd` instances within containers to
 create a mini development cluster. All state is saved between instances using a
-shared value.
+shared volume.
 
 Current workflow is big because we recreate the whole network by ourselves,
 next versions will use the started `btcd` bitcoin node in `testnet` and