github: add bug report template link to repro advice

Hopefully this will improve the quality of bug reports, making it easier
for someone investigating the issue to reliably repro the issue in the
first place, but then also create test cases off the back of the issue.

We keep the advice in a wiki for now until such time as that stabilises.

Change-Id: I876299e95381d46e9d7cb142e9ee11800cb440fa
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/9101
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/.github/ISSUE_TEMPLATE/bug_report.md b/.github/ISSUE_TEMPLATE/bug_report.md
index 781a070..d0b0420 100644
--- a/.github/ISSUE_TEMPLATE/bug_report.md
+++ b/.github/ISSUE_TEMPLATE/bug_report.md
@@ -31,6 +31,10 @@
 
 <!--
 If possible, provide a recipe for reproducing the error.
+
+For advice on how to create a good reproducer, please see:
+
+https://github.com/cuelang/cue/wiki/Creating-test-or-performance-reproducers
 -->