update: organize commands to subcommands and rename bin

- existing functions are moved to subcommand `add-master-log`

README.md

@@ -9,6 +9,11 @@ cargo build
 cargo run -- -h
 ```
 
+Build for JATHub using cross:
+```sh
+CROSS_CONTAINER_ENGINE=podman cross build --release --target armv7-unknown-linux-musleabihf
+```
+
 ### test
 ```sh
 cargo test