doc: Suggest keys.openpgp.org as keyserver in SECURITY.md

This is in line with 4c43b7d from
PR #22688.

Author: real-or-random

SECURITY.md

@@ -17,4 +17,4 @@ The following keys may be used to communicate sensitive information to developer
 | 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.
+You can import a key by running the following command with that individual’s fingerprint: `gpg --keyserver hkps://keys.openpgp.org --recv-keys "<fingerprint>"` Ensure that you put quotes around fingerprints containing spaces.