docs: add GEMINI.md with agent instructions

Introduces GEMINI.md to provide high-level instructional context for
AI agents. This ensures future interactions respect the project’s
primary documentation, execution paths via Makefile, and TDD-based
development process.

Author: rnovatorov

GEMINI.md

@@ -0,0 +1,5 @@
+# Enapter Python SDK Instructions
+
+- **Project Information:** Refer to `README.md` for details about the project.
+- **Execution Commands:** Refer to `Makefile` for all commands required to build, test, and lint the project. Always use the provided commands instead of running underlying tools directly.
+- **Development Process:** This project follows Test-Driven Development (TDD). Always write or update tests before or alongside implementation code.