Explain hci effect tests

dev/flake-module.nix

@@ -12,6 +12,7 @@
       nativeBuildInputs = [
         pkgs.nixpkgs-fmt
         pkgs.pre-commit
+        pkgs.hci
       ];
       shellHook = ''
         ${config.pre-commit.installationScript}

dev/tests/README.md

@@ -0,0 +1,15 @@
+
+# Running the tests
+
+These tests can be run locally with the `hci effect run` command. This gives
+the tests access to a proper nix daemon and the network.
+
+Designed for convenient deployments, it needs some information from git. You
+may use `--no-token` to disable this functionality if you're getting errors, or
+if you're asked to log in.
+
+Example:
+
+```console
+hci effect run --no-token default.effects.tests.template
+```