Add support for docs repo to update-user-guides target

The script is run inside a container that does not have access to
the repo checkout, so moved the copy logic into the Makefile.

Renamed script to accurately reflect its revised purpose.

Makefile

@@ -290,11 +290,15 @@ list-translators:  ## Collect the names of translators since the last merge from
 list-all-translators:  ## Collect the names of all translators in the project's history.
 	@$(DEVSHELL) $(SDROOT)/securedrop/i18n_tool.py list-translators --all
 
-# TODO: test this to make sure the paths in update-user-guides work
 .PHONY: update-user-guides
-update-user-guides:  ## Run the page layout tests to regenerate screenshots.
-	@echo "Running page layout tests to update guide screenshots..."
-	@$(DEVSHELL) $(SDBIN)/update-user-guides
+update-user-guides:  ## Regenerate docs screenshots. Set DOCS_REPO_DIR to repo checkout root.
+ifndef DOCS_REPO_DIR
+	$(error DOCS_REPO_DIR must be set to the documentation repo checkout root.)
+endif
+	@echo "Running page layout tests to update screenshots used in user guide..."
+	@$(DEVSHELL) $(SDBIN)/generate-docs-screenshots
+	@echo "Copying screenshots..."
+	cp securedrop/tests/pageslayout/screenshots/en_US/*.png $${DOCS_REPO_DIR}/docs/images/manual/screenshots
 	@echo
 
 

securedrop/bin/update-user-guides → securedrop/bin/generate-docs-screenshots

@@ -15,4 +15,3 @@ maybe_create_config_py
 
 ./i18n_tool.py translate-messages --compile
 pytest -v --page-layout "${@:-tests/pageslayout}"
-cp tests/pageslayout/screenshots/en_US/*.png ../docs/images/manual/screenshots