readme: added mount point for encfs password

README.md

@@ -2,6 +2,8 @@
 # TODO remove --privileged
 # TODO remoge --userns
 # TODO add image name
-docker run --rm -it -v plain-data:/source/plain \
+docker run --rm -it \
+    -v plain-data:/source/plain \
+    -v encfs-password:/source/secret \
     --device /dev/fuse --privileged --userns host ?
 ```