Move directory for nat loopback and add notice

1. Move `nat-loopback-issues` from self-host/rustdesk-server-oss/ to self-host/
2. Add notice and article link to `self-host/rustdesk-server-oss/_index.en.md`` and `self-host/rustdesk-server-pro/_index.en.md`

content/self-host/nat-loopback-issues/_index.en.md

@@ -1,6 +1,7 @@
 ---
 title: NAT Loopback issues
-weight: 23
+weight: 500
+pre: "<b>2.5. </b>"
 ---
 {{% notice note %}}
 This explanation involves complex networking knowledge, we need your assistance to improve its readability.

content/self-host/rustdesk-server-oss/_index.en.md

@@ -7,3 +7,7 @@ pre: "<b>2.1. </b>"
 Please join our [Discord](https://discord.com/invite/nDceKgxnkV) if you would like to talk with us about self-hosting your own [open source RustDesk Server](https://github.com/rustdesk/rustdesk-server).
 
 {{% children depth="3" showhidden="true" %}}
+
+{{% notice note %}}
+If you build you own server on your home/office, and can't connect it though public IP/domain, please check [this article](https://rustdesk.com/docs/en/self-host/nat-loopback-issues/).
+{{% /notice %}}

content/self-host/rustdesk-server-pro/_index.en.md

@@ -21,7 +21,9 @@ RustDesk Server Pro has more features compared to the open source version.
 {{% notice note %}}
 RustDesk Client ≥ 1.2.0 required
 {{% /notice %}}
-
+{{% notice note %}}
+If you build you own server on your home/office, and can't connect it though public IP/domain, please check [this article](https://rustdesk.com/docs/en/self-host/nat-loopback-issues/).
+{{% /notice %}}
 ### Hardware requirement
 
 Lowest level VPS is enough for your use case. The server software is not CPU and memory intensive. Our public ID server hosted on a 2 CPU/4 GB Vultr server serves 1.5+ million endpoints.