doc: update SECURITY.md inline with recent changes to bitcoincore.org

See bitcoin-core/bitcoincore.org#809 and
bitcoin-core/bitcoincore.org#819 and
https://bitcoincore.org/en/contact/.

SECURITY.md

@@ -7,4 +7,14 @@ security updates: https://bitgesell.ca
 
 ## Reporting a Vulnerability
 
-To report security issues send an email to it@bitgesell.ca
+To report security issues send an email to security@bitcoincore.org (not for support).
+
+The following keys may be used to communicate sensitive information to developers:
+
+| Name | Fingerprint |
+|------|-------------|
+| Wladimir van der Laan | 71A3 B167 3540 5025 D447  E8F2 7481 0B01 2346 C9A6 |
+| Pieter Wuille | 133E AC17 9436 F14A 5CF1  B794 860F EB80 4E66 9320 |
+| Michael Ford | E777 299F C265 DD04 7930  70EB 944D 35F9 AC3D B76A |
+
+You can import a key by running the following command with that individual’s fingerprint: `gpg --recv-keys "<fingerprint>"` Ensure that you put quotes around fingerprints containing spaces.