Refine PULL_REQUEST_TEMPLATE.md

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,15 +1,18 @@
 <!-- YOU HAVE TO MODIFY THIS TEXT TO FIT YOUR PR. OTHERWISE, YOUR PR WILL BE CLOSED WITHOUT FURTHER COMMENT. -->
 
 Describe the changes you have made here: what, why, ...
+For a draft pull request, please outline what is your next steps. Do you need feedback? Will you continue in parallel? ...
 
 <!-- LINK THE ISSUE WITH THE "Closes" KEYWORD -->
 <!-- Example: Closes (link) OR Closes #xyz -->
 
 ### Mandatory checks
 
 <!--
-- Go through the list below. Please don't remove any items.
-- [x] done; [ ] not done / not applicable
+This checklist is mandatory even if you submit a draft pull request.
+For instance, when adding a UUI functionality, a screenshot helps reviewing - even if your code is not 100% complete.
+
+Go through the list below. Keep all items. Mark them as follows: [x] done or [ ] not done / not applicable
 -->
 
 - [x] I own the copyright of the code submitted and I licence it under the [MIT license](https://github.com/JabRef/jabref/blob/main/LICENSE)