chore: readme troubleshooting notes

Author: NathanWalker

README.md

@@ -4,3 +4,23 @@ Unit test runner for NativeScript
 Refer to the documentation of NativeScript CLI's `ns test init` command for usage.
 
 If you encounter an issue, please log it at https://github.com/NativeScript/nativescript-cli/
+
+### Troubleshooting
+
+If you see an error like this:
+
+```
+Error: connect ECONNREFUSED ::1:9876
+    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1195:16)
+```
+
+When using node 17 or higher, make sure your `karma.conf.js` contains a server hostname setting, for example:
+
+```
+// web server hostname (ensure this is present)
+hostname: '127.0.0.1',
+
+// web server port
+port: 9876,
+```
+See [here](https://github.com/NativeScript/nativescript-cli/commit/81cb9c37cdd4e24115be79b24b68dfbaf8cdcfd2) for changeset in CLI which adds that to all newly initialized unit test setups.