Reduce header levels in ISSUE_TEMPLATE.md

.github/ISSUE_TEMPLATE.md

@@ -1,26 +1,26 @@
 Subject: <what happen when you do on which document project>
 
-# Problem
+### Problem
 - <Detail of problem>
 
-## Procedure to reproduce the problem
+#### Procedure to reproduce the problem
 ```
 <Paste your command-line here which cause the problem>
 ```
 
-## Error logs / results
+#### Error logs / results
 ```
 <Paste your error log here>
 ```
 - <public link of unexpected result if you have>
 
-## Expected results
+#### Expected results
 <Describe what to actually do>
 
-# Reproducible project / your project
+### Reproducible project / your project
 - <link to your project, or attach zipped small project sample>
 
-# Environment info
+### Environment info
 - OS: <Unix/Linux/Mac/Win/other with version>
 - Python version:
 - Sphinx version: