fix: add more details to pull request template

Co-authored-by: Maël Imhof <mael.imhof@protonmail.com>

Author: Wylwi

.github/pull_request_template.md

@@ -1,4 +1,9 @@
 # Summary
 
+- What is the objective? What is fixed/what feature is added/what was documented?
+- How is the objective implemented? What classes/doc files/CI were changed?
 # Details
 
+Depends on the nature of the PR :
+- **Code changes :** describe the conceptual approach taken in the code and tell the reviewer what part of the changes does what, so that it's easier to read the code
+- **Other changes :** Add details if relevant, or remove this section if not useful