Add Greek folder

[feirw]

Summary

• Added a Greek translation of Day 1 (Introduction) in Greek/readme.md, matching the English lesson structure, images, and exercises.
• Included Greek/01_Day_Introduction/helloworld.py as the Day 1 example script.
• Added a Greek language link in the English README so the translation is easy to find.

Test plan

• Open Greek/readme.md in preview and confirm all images load.
• Check headings, code blocks, and Day 2 / language links.
• Run Greek/01_Day_Introduction/helloworld.py.
• Confirm the 🇬🇷 Ελληνικά link in the root readme.md opens the Greek Day 1 page.