feat: add Jekyll GitHub Pages setup

Add _config.yml with Cayman theme and index.md that includes
README.md content, enabling GitHub Pages without duplication.

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

_config.yml

@@ -0,0 +1,4 @@
+title: Penny-Pincher Provider
+description: A curated list of affordable (or almost free) LLM providers
+theme: jekyll-theme-cayman
+show_downloads: false

index.md

@@ -0,0 +1,4 @@
+---
+layout: default
+---
+{% include_relative README.md %}