update bug report issue template

Author: Young-Flash

.github/ISSUE_TEMPLATE/bug_report.md

@@ -23,3 +23,9 @@ Otherwise please try to provide information which will help us to fix the issue
 **rustc version**: (eg. output of `rustc -V`)
 
 **relevant settings**: (eg. client settings, or environment variables like `CARGO`, `RUSTC`, `RUSTUP_HOME` or `CARGO_HOME`)
+
+**code snippet to reproduce**: 
+```rust
+// add your code here
+
+```