add more config/setup info to readme

README.md

@@ -25,7 +25,30 @@ transbeam is configured with the following environment variables:
 - `STATIC_DIR`: path where the web app's static files live (default: `./static`)
 - `PORT`: port to listen on localhost for http requests (default: 8080)
 
-## installation
+It also uses the
+[`env_logger`](https://docs.rs/env_logger/latest/env_logger/) crate
+for logging; log levels are configured via the `RUST_LOG` variable,
+see `env_logger`'s documentation for details.
+
+## running
+
+### nix flakes
+
+```
+nix run git+https://git.xeno.science/xenofem/transbeam?ref=main
+```
+
+(The Nix package is wrapped with `STATIC_DIR` set automatically to the
+correct Nix store path, so it'll serve the static files properly
+no matter what directory you run it from.)
+
+### non-nix
+
+```
+git clone https://git.xeno.science/xenofem/transbeam
+cd transbeam
+cargo run --release
+```
 
 ## todo