README: split up into docs

docs/development.md

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+# Development and testing
+
+Ensure you have a [rust toolchain](https://www.rust-lang.org/tools/install) installed.
+
+In order to set up a test instance of mariadb in a docker container, run the following command:
+
+```bash
+docker run --rm --name mariadb -e MYSQL_ROOT_PASSWORD=secret -p 3306:3306 -d mariadb:latest
+```
+
+This will start a mariadb instance with the root password `secret`, and expose the port 3306 on the host machine.
+
+Run the following command to create a configuration file with the default settings:
+
+```bash
+cp ./example-config.toml ./config.toml
+```
+
+If you used the docker command above, you can use these settings as is, but if you are running mariadb/mysql on another host, port or with another password, adjust the corresponding fields in `config.toml`.
+This file will contain your database password, but is ignored by git, so it will not be committed to the repository.
+
+You should now be able to connect to the mariadb instance, after building the program and using arguments to specify the config file.
+
+```bash
+cargo run -- --config-file ./config.toml <args>
+
+# example usage
+cargo run -- --config-file ./config.toml create-db "${USER}_testdb"
+cargo run -- --config-file ./config.toml create-user "${USER}_testuser"
+cargo run -- --config-file ./config.toml edit-privs -p "${USER}_testdb:${USER}_testuser:A"
+cargo run -- --config-file ./config.toml show-privs
+```
+
+To stop and remove the container, run the following command:
+
+```bash
+docker stop mariadb
+```
+
+## Development using Nix
+
+If you have nix installed, you can easily test your changes in a NixOS vm by running:
+
+```bash
+nix run .#vm
+```
+
+You can configure the vm in `flake.nix`
+
+## Filter logs by user with journalctl
+
+If you want to filter the server logs by user, you can use journalctl's built-in filtering capabilities.
+
+```bash
+journalctl -eu muscl F_USER=<username>
+```