Add docs for ntfy alerts (#4779)

alerts/ntfy.md

@@ -0,0 +1,29 @@
+# ntfy
+
+![](../.gitbook/assets/ntfy-logo.png)
+
+[ntfy] (pronounced notify) is a simple HTTP-based pub-sub notification service. It allows you to send notifications to your phone or desktop via scripts from any computer, and/or using a REST API.
+
+## Configuring ntfy Alerts
+
+1. **Subscribe to a topic**: for example, on desktop:
+
+   ![ntfy Topic Subscription](../.gitbook/assets/ntfy_subscribe.png)
+
+2. **Turn on ntfy alerts** in the [LinuxGSM settings](../configuration/linuxgsm-config.md). \(`~/lgsm/config-lgsm/<gameserver>/common.cfg`\)
+
+_Note: The only required setting is to turn on `ntfyalert`, and set `ntfytopic` a unique topic if you are not selfhosting ntfy._
+
+```text
+# ntfy Alerts | https://docs.linuxgsm.com/alerts/ntfy
+ntfyalert="on"
+ntfytopic="your-topic-name" # Defaults to "LinuxGSM", you should use something unique.
+ntfyserver="selfhosted-ntfy-url" # Defaults to "https://ntfy.sh", set if self-hosting ntfy.
+ntfypriority=""
+ntfytags=""
+
+# If publishing to topics behind auth: https://docs.ntfy.sh/publish/#authentication
+ntfytoken=""
+ntfyusername=""
+ntfypassword=""
+```