docs: update feature request template

Author: streamtw

.github/ISSUE_TEMPLATE/feature_request.md

@@ -4,14 +4,14 @@ about: Suggest an idea for this project
 
 ---
 
-**Is your feature request related to a problem? Please describe.**
+## Is your feature request related to a problem? Please describe.
 A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
 
-**Describe the solution you'd like**
+## Describe the solution you'd like
 A clear and concise description of what you want to happen.
 
-**Describe alternatives you've considered**
+## Describe alternatives you've considered
 A clear and concise description of any alternative solutions or features you've considered.
 
-**Additional context**
+## Additional context
 Add any other context or screenshots about the feature request here.