Add ephemeral peer (#87)

Co-authored-by: Zoltan Papp <[email protected]>

src/pages/how-to/register-machines-using-setup-keys.mdx

@@ -17,6 +17,11 @@ There are 2 types of setup keys:
 * **One-off key**. This type of key can be used only once to authenticate a machine.
 * **Reusable key**. This type of key can be used multiple times to authenticate machines.
 
+## Ephemeral peers
+
+You can create a setup key with the ephemeral peers option enabled.
+Peers that are offline for over 10 minutes will be removed automatically.
+
 ## Using setup keys
 
 Setup keys are available in the NetBird Management Dashboard under the `Setup Keys` tab [https://app.netbird.io/setup-keys](https://app.netbird.io/setup-keys).
@@ -78,4 +83,4 @@ After your key has been successfully created, copy and store it in a secure loca
 
 <p>
     <img src="/docs-static/img/how-to-guides/setup-key-created.png" alt="high-level-dia" className="imagewrapper"/>
-</p>
+</p>