add docs for publishing to github pages manually

book-example/src/continuous-integration.md

@@ -54,3 +54,35 @@ deploy:
 ```
 
 That's it!
+
+### Deploying to GitHub Pages manually
+
+If you're CI doesn't support a GitHub pages, or you're deploying somewhere else
+with GitHub pages like integration, *note: you may want to use different tmp dirs*:
+
+```console
+$> git worktree add /tmp/book gh-pages
+$> mdbook build
+$> rm -rf /tmp/book/* # this won't delete the .git directory
+$> cp -rp book/* /tmp/book/
+$> cd /tmp/book
+$> git add -A
+$> git commit 'new book message'
+$> git push origin gh-pages
+$> cd -
+```
+
+Or put this into a Makefile rule:
+
+```makefile
+.PHONY: deploy
+deploy: book
+	@echo "====> deploying to github"
+	git worktree add /tmp/book gh-pages
+	rm -rf /tmp/book/*
+	cp -rp book/* /tmp/book/
+	cd /tmp/book && \
+		git add -A && \
+		git commit -m "deployed on $(shell date) by ${USER}" && \
+		git push origin gh-pages
+```