fix(docs): replace dead Build-a-Reddit-Bot link with Wayback snapshot

[Ankur-Kataria]

What is this?

Docs-only fix for a broken link in the Python / Bots section, reported in issue #761.

• Title: Build a Reddit Bot
• Original URL: https://www.pythonforengineers.com/blog/build-a-reddit-bot-part-1/
  consistently times out (domain unreachable)
• Replacement URL: Wayback Machine snapshot from April 2026
  http://web.archive.org/web/20260428033759/https://pythonforengineers.com/blog/build-a-reddit-bot-part-1/
  — returns HTTP 200 and preserves the full multi-part tutorial.
• Section: Python → Bots

python3 scripts/check_readme.py lint exits with errors=0 warnings=0.

Checklist

• This PR adds/fixes exactly one tutorial (or is a docs/tooling-only change).
• Free and open -- no paywall, login wall, or required newsletter signup.
• Project-based -- following it, the reader builds a complete, working artifact.
• I searched README.md for this URL and title -- it is not already listed.
• Entry uses - [Title](https://...) format, placed under the correct section (nested - [Part N](...) for multi-part series).
• No URL shorteners.
• I ran python3 scripts/check_readme.py lint locally and it exits 0.
• Relationship disclosure: no relationship to the author.

Fixes #761