Update generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent.md (#908)

* Update generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent.md

I ran the steps today on mac OS Catalina and it did not work for me. I had to make two changes that I updated in the doc.

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

Co-authored-by: hubwriter <hubwriter@github.com>

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

Add space between sentences, plus slight rewording.

Co-authored-by: hubwriter <hubwriter@github.com>

Author: poonam-lamba

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

@@ -98,13 +98,19 @@ Before adding a new SSH key to the ssh-agent to manage your keys, you should hav
         IdentityFile ~/.ssh/id_ed25519
       ```
 
+     {% note %}
+
+     **Note:** If you chose not to add a passphrase to your key, you should omit the `UseKeychain` line.
+  
+     {% endnote %}
+  
 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
    $ ssh-add -K ~/.ssh/id_ed25519
   ```
   {% note %}
 
-  **Note:** The `-K` option is Apple's standard version of `ssh-add`, which stores the passphrase in your keychain for you when you add an ssh key to the ssh-agent.
+  **Note:** The `-K` option is Apple's standard version of `ssh-add`, which stores the passphrase in your keychain for you when you add an ssh key to the ssh-agent. If you chose not to add a passphrase to your key, run the command without the `-K` option. 
 
   If you don't have Apple's standard version installed, you may receive an error. For more information on resolving this error, see "[Error: ssh-add: illegal option -- K](/articles/error-ssh-add-illegal-option-k)."