'security-announcements' mailing list does not exist

[lukpueh]

The 'Security Advisories' page mentions the mailing list 'security-announcements', but the list does not exist:

security-handbook/docs/vulnerabilities/advisories.md

Line 85 in e382b05

- An announcement mailing list (the Eclipse Foundation provides a security-announcements@ mailing list, open for everyone to subscribe. Projects may opt to create their own announcement mailing list or use their usual communication channels directed towards their users).

The list should either be created or not mentioned. If the list is created, we could add a subscription link (and maybe drop the stray @, or spell out the full address).