Pull Request template: require forks to provide a list of differences to the original (#3998)

- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/pull/3467

.github/PULL_REQUEST_TEMPLATE.md

@@ -25,6 +25,7 @@ To ensure your PR is dealt with swiftly please check the following:
 - [ ] Any software project you are adding to the list is actively maintained.
 - [ ] Any software project you are adding was first released more than 4 months ago.
 - [ ] Any software project you are adding has working installation instructions.
+- [ ] If you are adding software forked from another project, please provide/link to a clear list of differences between both.
 - [ ] The pull request title is informative, unlike "Update README.md".
   Suggested titles: "Add aaa to bbb" for adding software aaa to section bbb,
   "Remove aaa from bbb" for removing, "Fix license for aaa", etc.