Manage → Security → Documents is the security-specific evidence checklist — things like your QA process documentation, a link to your public status page, proof of customer data deletion, your pseudonymization procedure, and backup/redundancy evidence:
This works exactly like Organisation Documents — same Evidence / Instructions / Details / Controls tabs on each item, same upload-a-file-or-link-a-URL-or-ticket mechanic, and the same Add Document option for tracking something custom that isn't already in the standard list. The only difference is the category of evidence: this page is specifically the security- and engineering-flavored checklist, separate from the HR-flavored items on the Organisation Documents page.
If you haven't already, see that article for the full walkthrough of providing evidence, using the Instructions tab, and adding a custom document with a recurrence schedule — it all applies here too.