Add SEO pillar page: Complete Guide to SEC Filings in Python

2000-word comprehensive guide covering installation, company lookup,
filings, financial statements, insider trading, 13F holdings, funds,
AI/MCP integration, and comparison with alternatives. Linked from
Get Started nav and cross-linked to 10+ Colab notebooks.

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

Author: dgunning