[Magic Firewall] Add note for existing rules (#22544)

Author: Maddy-Cloudflare

src/content/docs/magic-firewall/how-to/add-rules.mdx

@@ -15,7 +15,7 @@ By default, you can create a maximum of 200 rules. We recommend you create lists
 1. Log in to your [Cloudflare dashboard](https://dash.cloudflare.com/login), and select your account.
 2. Select **Magic Firewall**.
 3. In the **Custom rules** tab, select **Add a Rule**.
-4. Fill out the information for your new rule. You can use a managed [IP list](https://www.cloudflare.com/en-gb/ips/) when populating the **Value**.
+4. Fill out the information for your new rule. All existing rules apply to IPv4. You can use a managed [IP list](https://www.cloudflare.com/en-gb/ips/) when populating the **Value**.
 5. When you are done, select **Add new rule**.
 
 ## Create a disabled rule