Revise our pull request template

The old one was far too long, meaning that most people would skip
over most of it. So let's focus on the important bits, which are
a useful description and release notes.

The stuff at the end for reviewers was not used by us in practice;
instead, there should be a separate document somewhere with guidelines
for reviewers.

.github/pull_request_template.md

@@ -1,58 +1,13 @@
-Please use the following template to submit a pull request, filling
-in at least the "Text for release notes" and/or "Further details".
-Thank you!
+Please provide a short summary of this PR and its purpose here. E.g., does it add a new feature, and which? Does it fix a bug, and which? If there is an associated issue, please list it here.
 
-# Description
+## Text for release notes
 
-## Text for release notes 
+We track noteworthy changes as entries in the `CHANGES.md` file in the root directory of this repository. To help us decide whether and how to describe your PR, please do one of the following:
 
-If this pull request shall **not** be mentioned in the release notes
-(to be distributed in the file `CHANGES.md`),
-please add the label `release notes: not needed`.
-
-Otherwise, please proceed in one of the following ways:
-
-- Choose a title that can serve as text for the release notes,
-  and add the label `release notes: use title`.
-
-- Put the text for the release notes **here**,
-  that is, between the markers `Text for release notes`
-  and `(End of text for release notes)`.
-
-The first variant is recommended whenever the text for release notes
-is suitable as title.
-
-In both cases, please follow the style of the GAP `CHANGES.md` file
-in the root directory.
-In particular, please surround the names of GAP functions with backquotes.
-
-## (End of text for release notes)
+1. If this PR shall **not** be mentioned in the release notes, write "none" here.
+2. If a brief note suffices, edit the title of this PR to be usable as entry in `CHANGES.md`, and write "see title" here (or if you have the required permissions, add the label `release notes: use title` to this PR and remove this section)
+3. If a longer note is needed, just write it here, ideally following the general style used in that file
 
 ## Further details
 
-If necessary, please provide further details here.
-
-# Checklist for pull request reviewers
-
-- [ ] proper formatting
-
-If your code contains kernel C code, run `clang-format` on it; the 
-simplest way is to use `git clang-format`, e.g. like this (don't
-forget to commit the resulting changes):
-
-    git clang-format $(git merge-base HEAD master)
-
-- [ ] usage of relevant labels
-
-   1. either `release notes: not needed` or `release notes: to be added`
-   2. at least one of the labels `bug` or `enhancement` or `new feature`
-   3. for changes meant to be backported to `stable-4.X` add the `backport-to-4.X` label
-   4. consider adding any of the labels `build system`, `documentation`, `kernel`, `library`, `tests`
-
-- [ ] runnable tests
-- [ ] lines changed in commits are sufficiently covered by the tests
-- [ ] adequate pull request title
-- [ ] well formulated text for release notes
-- [ ] relevant documentation updates
-- [ ] sensible comments in the code
-
+If necessary, provide further details down here.