Refine PULL_REQUEST_TEMPLATE.md (#12749)

* Refine PULL_REQUEST_TEMPLATE.md

* Refinements

* Thilo's suggestions

* Remove redundant text

* Refine screenshot check

* Tiny refinement

* Unify same information

* Refine WIP comment

* Update .github/PULL_REQUEST_TEMPLATE.md

Co-authored-by: ThiloteE <[email protected]>

* Update .github/PULL_REQUEST_TEMPLATE.md

* refine first few lines

* one more underscore

* xyz -> numbers

---------

Co-authored-by: Subhramit Basu <[email protected]>
Co-authored-by: ThiloteE <[email protected]>

Author: 3 people

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,21 +1,27 @@
-<!-- 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, ...
+<!-- YOU HAVE TO MODIFY THE TEXT BELOW TO FIT YOUR PR. OTHERWISE, YOUR PR WILL BE CLOSED WITHOUT FURTHER COMMENT. -->
 
 <!-- LINK THE ISSUE WITH THE "Closes" KEYWORD -->
-<!-- Example: Closes (link) OR Closes #xyz -->
+<!-- Example: Closes (link) OR Closes #12345 -->
+
+Closes _____
+Describe the changes you have made here: what, where, why, ...
+If your work is not yet complete, please open a draft pull request. In that case, outline your intended next steps. Do you need feedback? Will you continue in parallel? ...
 
 ### Mandatory checks
 
 <!--
-- Go through the list below. Please don't remove any items.
-- [x] done; [ ] not done / not applicable
+Go throgh the checklist below. It is mandatory, even for a draft pull request.
+
+Keep ALL the items. Mark them as follows: 
+[x] done 
+[ ] 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)
 - [ ] Change in `CHANGELOG.md` described in a way that is understandable for the average user (if change is visible to the user)
 - [ ] Tests created for changes (if applicable)
 - [ ] Manually tested changed features in running JabRef (always required)
-- [ ] Screenshots added in PR description (for UI changes)
+- [ ] Screenshots added in PR description (if change is visible to the user)
 - [ ] [Checked developer's documentation](https://devdocs.jabref.org/): Is the information available and up to date? If not, I outlined it in this pull request.
 - [ ] [Checked documentation](https://docs.jabref.org/): Is the information available and up to date? If not, I created an issue at <https://github.com/JabRef/user-documentation/issues> or, even better, I submitted a pull request to the documentation repository.