Add details to SSH key restrictions documentation

doc/security/ssh_keys_restrictions.md

@@ -36,6 +36,16 @@ An icon is visible to the user of a restricted key in the SSH keys section of th
 
 Hovering over this icon tells you why the key is restricted.
 
+## Default settings
+
+By default, the GitLab.com and self-managed settings for the
+[supported key types](../ssh/index.md#supported-ssh-key-types) are:
+
+- RSA SSH keys are allowed.
+- DSA SSH keys are forbidden ([since GitLab 11.0](https://about.gitlab.com/releases/2018/06/22/gitlab-11-0-released/#support-for-dsa-ssh-keys)).
+- ECDSA SSH keys are allowed.
+- ED25519 SSH keys are allowed.
+
 <!-- ## Troubleshooting
 
 Include any troubleshooting steps that you can foresee. If you know beforehand what issues

doc/user/gitlab_com/index.md

@@ -9,6 +9,10 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 This page contains information about the settings that are used on GitLab.com, available to
 [GitLab SaaS](https://about.gitlab.com/pricing/) customers.
 
+## SSH key restrictions
+
+GitLab.com uses the default [SSH key restrictions](../../security/ssh_keys_restrictions.md).
+
 ## SSH host keys fingerprints
 
 Below are the fingerprints for SSH host keys on GitLab.com. The first time you