Add KNOWN_HOSTS entry to GitLab.com settings

- Document the entry for ssh `known_hosts` file for users who want to
  directly accept the proper keys without manual invocation
Signed-off-by: Robert Marshall <rmarshall@gitlab.com>

doc/user/gitlab_com/index.md

@@ -14,6 +14,17 @@ Below are the fingerprints for GitLab.com's SSH host keys.
 |  ED25519  | `2e:65:6a:c8:cf:bf:b2:8b:9a:bd:6d:9f:11:5c:12:16` | `eUXGGm1YGsMAS7vkcx6JOJdOGHPem5gQp4taiCfCLB8` |
 |  RSA      | `b6:03:0e:39:97:9e:d0:e7:24:ce:a3:77:3e:01:42:09` | `ROQFvPThGrW4RuWLoL9tq9I9zJ42fK4XywyRtbOz/EQ` |
 
+## SSH `known_hosts` entries
+
+Add the following to `.ssh/known_hosts` to skip manual fingerprint
+confirmation in SSH:
+
+```
+gitlab.com ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAfuCHKVTjquxvt6CM6tdG4SLp1Btn/nOeHHE5UOzRdf
+gitlab.com ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCsj2bNKTBSpIYDEGk9KxsGh3mySTRgMtXL583qmBpzeQ+jqCMRgBqB98u3z++J1sKlXHWfM9dyhSevkMwSbhoR8XIq/U0tCNyokEi/ueaBMCvbcTHhO7FcwzY92WK4Yt0aGROY5qX2UKSeOvuP4D6TPqKF1onrSzH9bx9XUf2lEdWT/ia1NEKjunUqu1xOB/StKDHMoX4/OKyIzuS0q/T1zOATthvasJFoPrAjkohTyaDUz2LN5JoH839hViyEG82yB+MjcFV5MU3N1l1QL3cVUCh93xSaua1N85qivl+siMkPGbO5xR/En4iEY6K2XPASUEMaieWVNTRCtJ4S8H+9
+gitlab.com ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBFSMqzJeV9rUzU4kWitGjeR4PWSa29SPqJ1fVkhtj3Hw9xjLVXVYrU9QlYWrOLXBpQ6KWjbjTDTdDkoohFzgbEY=
+```
+
 ## Mail configuration
 
 GitLab.com sends emails from the `mg.gitlab.com` domain via [Mailgun] and has