Update README.md

Arun-Rocker · web-flow · commit 78942e7ab393 · 2025-05-04T19:10:50.000+05:30
diff --git a/Day-05/README.md b/Day-05/README.md
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+Environment variables are a fundamental way to configure applications without hardcoding sensitive or environment-specific values. 
+Here's a comprehensive guide to working with environment variables in Python.
+
+Linux/macOS:
+export DB_HOST="localhost"
+
+import os
+
+# Simple get with optional default
+api_key = os.getenv('API_KEY', 'default-key')
