add short readme

README.md

@@ -0,0 +1,37 @@
+# Hesinde Sync
+
+A reimplementation of the
+[Koreader Sync Server](https://github.com/koreader/koreader-sync-server) because
+I wanted to try
+[poem openapi](https://docs.rs/poem-openapi/latest/poem_openapi/).
+
+# Building
+
+## Nix
+
+A [nix](https://nixos.org/download/) environment with enabled
+[nix-commands](https://nixos.wiki/wiki/Flakes) in order to use `nix develop`.
+
+Run `nix develop` to be dropped into a shell with everything installed and
+configured. From there all the usual `cargo` commands are accessible.
+
+## Classic
+
+A recent [rust](https://www.rust-lang.org/learn/get-started) installation is all
+that is needed.
+
+From there on `cargo run` and `cargo build` and so on can be used.
+
+# Usage
+
+```
+Usage: hesinde-sync [OPTIONS]
+
+Options:
+  -a, --address <ADDRESS>              Address to listen on [env: ADDRESS=] [default: localhost:3030]
+  -d, --db-connection <DB_CONNECTION>  From which file to read the database connection string ("-" for stdin) [env: DB_CONNECTION=] [default: -]
+  -h, --help                           Print help
+  -V, --version                        Print version
+```
+
+The url for koreader is `http://<ADDRESS>/api`.