clarified ssh options

README.md

@@ -63,7 +63,7 @@ brew install hcloud
 ### 💡 [Do not skip] Creating the terraform.tfvars file
 
 1. Create a project in your [Hetzner Cloud Console](https://console.hetzner.cloud/), and go to **Security > API Tokens** of that project to grab the API key. Take note of the key! ✅
-2. Either, generate a passphrase-less ed25519 SSH key-pair for your cluster, unless you already have one that you'd like to use. Take note of the respective paths of your private and public keys. Or, for a key-pair with passphrase or a device like a Yubikey, make sure you have have an SSH agent running and your key is loaded (`ssh-add -L` to verify) and set `private_key = null` in the following step. ✅
+2. Generate a passphrase-less ed25519 SSH key-pair for your cluster, take note of the respective paths of your private and public keys. Or, see our detailed [SSH options](https://github.com/kube-hetzner/kube-hetzner/blob/master/docs/ssh.md). ✅
 3. Copy `terraform.tfvars.example` to `terraform.tfvars`, and replace the values from steps 1 and 2. ✅
 4. Make sure you have the latest Terraform version, ideally at least 1.1.0. You can check with `terraform -v`. ✅
 5. (Optional) There are other variables in `terraform.tfvars` that could be customized, like Hetzner region, and the node counts and sizes.

docs/ssh.md

@@ -0,0 +1,24 @@
+Kube-Hetzner requires you to have a recent version of OpenSSH (>=6.5) installed on your client, and the use of a key-pair generated with either of the following algorithms:
+
+- ssh-ed25519 (preferred, and most simple to use without passphrase)
+- rsa-sha2-512
+- rsa-sha2-256
+
+If your key-pair is of the `ssh-ed25519` sort, and without of passphrase, you do not need to do anything else. Just set `public_key` and `private_key` to their respective path values in your terraform.tfvars.
+
+---
+
+Otherwise, for a key-pair with passphrase or a device like a Yubikey, make sure you have have an SSH agent running and your key is loaded with:
+
+```bash
+eval ssh-agent $SHELL
+ssh-add ~/.ssh/my_private-key_id
+```
+
+Verify it is loaded with:
+
+```bash
+ssh-add -l
+```
+
+Then set `private_key = null` in your terraform.tfvars, as it will be read from the ssh-agent automatically.