feat: add self-update command and bump to 2.0.1

- Add `coinhunter update` CLI command for pipx/pip upgrade
- README: document update behavior and recommend pipx install
- Dynamic version badge with cacheSeconds=60
- Version bump: 2.0.0 → 2.0.1

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "coinhunter"
-version = "2.0.0"
+version = "2.0.1"
 description = "Binance-first trading CLI for balances, market data, opportunity scanning, and execution."
 readme = "README.md"
 license = {text = "MIT"}