Add issue template for bug reports (#1185)

Reminds users to look attach the `--record` output.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,20 @@
+---
+name: Bug report
+about: Create a report to help us improve Verus
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+<!-- 
+
+Thanks for helping improve Verus!
+
+In addition to describing the issue, please consider using the `--record` feature to produce a zip file (containing a copy of your crate, along with relevant metadata such as Verus command line arguments), to attach to the issue to help us reproduce it. See https://github.com/verus-lang/verus/blob/main/CONTRIBUTING.md for more details.
+
+If you cannot (for any reason) attach your crate's source for reproducing, consider including a minimized example, along with your `verus --version`.  We have some support for automatic minimization of issues. See https://github.com/verus-lang/verus/tree/main/source/tools/minimizers for more details.
+
+For feature requests, please use the Discussions page (https://github.com/verus-lang/verus/discussions).  We suggest adding a comment if you can find a relevant discussion, but feel free to open a new discussion in the "Feature Requests" category (https://github.com/verus-lang/verus/discussions/categories/feature-requests).
+
+ -->