docs(ssh): Improve note about existing keys

docs/ssh.md

@@ -24,7 +24,7 @@ To be able to clone your project from the [TU Graz GitLab](https://gitlab.tugraz
 
 Next steps: [Generating a new SSH key](#generating-a-new-ssh-key)
 
-> If you have already generated an SSH key, keep in mind to add it to the ssh-agent.
+> If you have already generated an SSH key, keep in mind to add it to the ssh-agent suing the `ssh-add` command. If you are not sure how to do this, simply follow all steps from the [Generating a new SSH key](#generating-a-new-ssh-key) section again. 
 
 ### MacOS
 
@@ -32,7 +32,7 @@ When using MacOS, the SSH authentication agent should be started automatically.
 
 Next steps: [Generating a new SSH key](#generating-a-new-ssh-key)
 
-> If you have already generated an SSH key, keep in mind to add it to the ssh-agent.
+> If you have already generated an SSH key, keep in mind to add it to the ssh-agent suing the `ssh-add` command. If you are not sure how to do this, simply follow all steps from the [Generating a new SSH key](#generating-a-new-ssh-key) section again. 
 
 ### Linux