Add online comparison resources to Testing Tools appendix

[appsecsanta]

What

Add an "Online Resources" section to Appendix A (Testing Tools Resource) linking to free tool comparison and testing resources.

Proposed additions

1. AppSec Santa — Free, curated comparison of 163+ application security tools across SAST, DAST, SCA, API Security, and 6 other categories. Helps practitioners evaluate and select testing tools.

2. AppSec Santa Security Headers Checker — Free interactive tool to analyze HTTP security headers for any URL.

Why

The Testing Tools appendix currently lists individual tools but has no section for comparison/evaluation resources. Practitioners researching which tool to use would benefit from a link to a comprehensive comparison alongside the individual tool listings.

Both resources are free to use, which aligns with the WSTG's policy of listing only freely available tools.

Proposed location

A new ## Online Resources section at the end of document/6-Appendix/A-Testing_Tools_Resource.md.

I can submit a PR if this addition is welcome.

[Nik-ui]

Hi @kingthorin ,

I am interested in working on this issue. Since it’s been open for a few weeks, I’d be happy to handle the implementation and open a PR for these additions.

Please let me know if I should go ahead!

[kingthorin]

This was covered by your last PR wasn't it?