Add contributor guide and project usage docs

tests/test_config.py

@@ -0,0 +1,11 @@
+"""Config 테스트."""
+
+from lazy_enter.config import Config
+
+
+def test_config_defaults():
+    config = Config()
+    assert config.default_shell == "claude"
+    assert config.pty_read_timeout == 5
+    assert config.output_buffer_interval == 2.0
+    assert config.max_message_length == 3000