docs: Rewrite issue template to discourage confused posts.
-[Read our guide on bug reports here](./ISSUES_GUIDE.md)
-
-**Actual Behaviour**
-
-Explain what is currently happening.
-
-**Expected Behaviour**
-
-Explain what you expected (unnecessary if it's obviouxly broken, e.g. a crash).
-
-**Would you like to work on the issue?**
-
-Let us know if this issue should be assigned to you.
+**Note**: This repository is for the 2014-era Zulip Android app; you
+probably are you using
+[zulip-mobile](https://github.com/zulip/zulip-mobile) and want to
+[report an issue here](https://github.com/zulip/zulip-mobile/issues).
