update bug template (#3902)

.github/ISSUE_TEMPLATE/bug_report.md

@@ -19,12 +19,8 @@ assignees: ''
 
 ### To Reproduce
 
-Steps to reproduce the behavior:
-
-1. Go to '...'
-2. Run '....'
-3. Scroll down to '....'
-4. See error
+Before reporting a bug, make sure that the bug can be reproduced with a minimal example. You can simply subclass our [miminal code example] (https://github.com/PyTorchLightning/pytorch-lightning/blob/master/pl_examples/bug_report_model.py) and add your relevant changes, to see if the issue persists. 
+If the test is failing, please add your test cases to the issue (as a draft PR, or simple paste the code to the isse description here).
 
 <!-- If you have a code sample, error messages, stack traces, please provide it here as well -->