Add README with uv install instructions, fix pyproject.toml

- Add README.md with install/run instructions using uv
- Add build-system and script entry point to pyproject.toml
- Add .gitignore for __pycache__ and save files
- Remove placeholder main.py (entry point is h2g2.main:main)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pyproject.toml

@@ -1,7 +1,14 @@
 [project]
 name = "h2g2"
 version = "0.1.0"
-description = "Add your description here"
+description = "The Hitchhiker's Guide to the Galaxy - Python text adventure engine"
 readme = "README.md"
-requires-python = ">=3.14"
+requires-python = ">=3.12"
 dependencies = []
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[project.scripts]
+h2g2 = "h2g2.main:main"