Block os.tc tracker as found on www.dreadcentral.com. Towards #937

trackers/os.tc/index.md

+# **OneSignal** (os.tc)
+
+> See [onesignal.com](/trackers/onesignal.com)
+
+## Ethical design violations
+
+(Learn more about [Ethical Design](https://ind.ie/ethical-design).)
+
+  * (Tracker)
+
+<!-- Other ethical design violation badges go here. Valid ones are:
+  * (Aggressive)
+  * (Doorslam)
+  * (Clickbait)
+  * (Fingerprint)
+  * (Web bug)
+-->
+
+<!-- If there are decentralised or more ethical alternatives to a cloud service, list them here.
+
+## Decentralised alternatives
+
+Decentralised, free and open alternatives that adhere better to the [Ethical Design Manifesto](https://ind.ie/ethical-design):
+
+  * None yet.
+
+-->
+
+## Block rule
+
+<!--
+	The original block rule is automatically generated by Better Inspector.
+	If you want to edit it, you may. The Inspector will not touch your edits
+	in future passes.
+-->
+
+**Block domain** os.tc
+
+```mson
+- trigger:
+	- url-filter: os.tc
+	- load-type: third-party
+- action:
+	- type: block
+```
+
+## Prevalence
+
+<!-- prevalence -->
+**Moderate:** found on 0.2% of surveyed sites (16 instances observed).
+<!-- /prevalence -->
+
+## Notes
+
+  * The domain is owned by OneSignal.