Update GitHub pull request template, because it also shows up on Gitea apparently.

.github/pull_request_template.md

@@ -1,6 +1,10 @@
-## Hold up!
+## Hold up, GitHub users
 
-Thanks for your contribution. Unfortunately, we don't use GitHub pull requests to manage code contributions to this repository (and GitHub doesn't have any way to disable pull requests entirely). Instead, please see:
+Thanks for your contribution! 
+
+If you're submitting this PR on **projects.torsion.org**: Please ignore the following. You can safely delete this text before submitting your PR.
+
+If you're submitting this PR on **GitHub**: Unfortunately, we don't use GitHub pull requests to manage code contributions to this repository (and GitHub doesn't have any way to disable pull requests entirely). Instead, please see:
 
 https://torsion.org/borgmatic/#contributing