Add note about permissions

README.md

@@ -2,3 +2,9 @@
 [![Latest build of the paper](https://img.shields.io/badge/PDF-latest-orange.svg?style=flat)](../gh-action-result/pdflatex/notes-template.pdf)
 
 This is a simple revtex LaTeX template (using JHEP.bst), and this repo uses github actions to automatically build the latest PDF. The result is linked above.
+
+If you use this repo template, GitHub will by default not enable
+actions to be able to push back to the repo, which is needed to store
+the PDF (in an orphan branch). To enable them, go to your repo's
+settings, go to Actions, then down to Workflow permissions, and enable
+'Read and write permissions'.