chore: stub workflow for automatic docs deployment

.github/workflows/docs.yml

@@ -0,0 +1,13 @@
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - main
+
+jobs:
+  publish_docs:
+    name: Publish latest documentation
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      # TODO: run makefile in docs directory, then commit built assets to gh-pages branch

doc/Makefile

@@ -70,9 +70,3 @@ linkcheck:
 	@echo
 	@echo "Link check complete; look for any errors in the above output " \
 	      "or in linkcheck/output.txt."
-
-gh-pages: html
-	cd gh-pages; git pull --rebase; cd ..; cp -r ./html/* gh-pages
-
-publish: gh-pages
-	cd gh-pages; git commit -a; git push; cd ..