minor modifications on the issue template (nvim-lua#244)

* use real markdown headers for section titles

* add a newline after the initial comment for readability

* make hint indications comments

.github/ISSUE_TEMPLATE/bug_report.md

@@ -8,19 +8,21 @@ assignees: ''
 ---
 
 <!-- Any bug report not following this template will be immediately closed. Thanks -->
-**Describe the bug**
-A clear and concise description of what the bug is.
 
-**To Reproduce**
-Steps to reproduce the behavior:
+## Describe the bug
+<!-- A clear and concise description of what the bug is. -->
+
+## To Reproduce
+<!-- Steps to reproduce the behavior. -->
 1. ...
 
-**Desktop (please complete the following information):**
+## Desktop
+<!-- please complete the following information. -->
 - OS: 
 - Terminal: 
 
-** Neovim Version **
- - Output of running `:version` from inside of neovim:
+## Neovim Version
+<!-- Output of running `:version` from inside of neovim. -->
 
 ```
 ```