add cargo doc

backend/readme.md

@@ -15,4 +15,11 @@ choco install -y rustup
 - `rustup-init.sh` (Windows: rustup-init.ex, e.g. %AppData%\Local\Temp\chocolatey\rustup.install\1.25.1\rustup-init.exe)
 - select a good match in the dialog of this CLI installer,
 - i.e. stable and default amount of features should be fine
+- rust comes with `cargo` as a ``crate'' manager for package installation
 
+## Get dependencies and run
+
+```shell
+cargo build # gets dependencies from Cargo.toml
+cargo run   #  re-runs on (some?) changes
+```