add additional information on dealing with ~/.ssh/config errors on Mac

content/github/authenticating-to-github/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent.md

@@ -105,6 +105,25 @@ Before adding a new SSH key to the ssh-agent to manage your keys, you should hav
      **Note:** If you chose not to add a passphrase to your key, you should omit the `UseKeychain` line.
 
      {% endnote %}
+
+      {% mac %}
+      {% note %}
+
+      **Note:** If you see an error like this
+
+      ```
+      /Users/USER/.ssh/config: line 16: Bad configuration option: usekeychain
+      ```
+
+      add an additional config line to your `Host *` section:
+
+      ```
+      Host *
+        IgnoreUnknown UseKeychain
+      ```
+
+      {% endnote %}
+      {% endmac %}
 
 3. Add your SSH private key to the ssh-agent and store your passphrase in the keychain. {% data reusables.ssh.add-ssh-key-to-ssh-agent %}
    ```shell