less screaming headlines for the template

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,28 +1,28 @@
 <!--- Provide a general summary of your changes in the Title above -->
 
-## Description
+### Description
 <!--- Describe your changes in detail -->
 
-## Motivation and Context
+### Motivation and Context
 <!--- Why is this change required? What problem does it solve? -->
 <!--- If it fixes an open issue, please link to the issue here. -->
 
-## How Has This Been Tested?
+### How Has This Been Tested?
 <!--- Please describe in detail how you tested your changes. -->
 <!--- Include details of your testing environment, and the tests you ran to -->
 <!--- see how your change affects other areas of the code, etc. -->
 
-## Screenshots (if appropriate):
+### Screenshots (if appropriate):
 
-## Types of changes
+### Types of changes
 <!--- What types of changes does your code introduce? Put an `x` in all the boxes that apply: -->
 - [ ] Bug fix (non-breaking change which fixes an issue)
 - [ ] New feature (non-breaking change which adds functionality)
 - [ ] Breaking change (fix or feature that would cause existing functionality to change)
 
-## Checklist:
+### Checklist:
 <!--- Go over all the following points, and put an `x` in all the boxes that apply. -->
 <!--- If you're unsure about any of these, don't hesitate to ask. We're here to help! -->
 - [ ] My code follows the code style of this project.
 - [ ] My change requires a change to the documentation.
-- [ ] I have updated the documentation accordingly.
+- [ ] I have updated the documentation accordingly.