Add GitHub Sponsors button to repository

Added FUNDING.yml to display sponsor button, linking to GitHub Sponsors
profile and danielmiessler.com/sponsor.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: danielmiessler

.github/FUNDING.yml

@@ -0,0 +1,5 @@
+# GitHub Sponsors configuration for Substrate
+# This adds a sponsor button to the repository
+
+github: danielmiessler
+custom: ["https://danielmiessler.com/sponsor"]