build(docs): check changes to rst files in Makefile

Makefile

@@ -188,10 +188,11 @@ dist/$(PACKAGE_NAME)-$(PACKAGE_VERSION)-build-epoch.txt:
 	echo $(SOURCE_DATE_EPOCH) > dist/$(PACKAGE_NAME)-$(PACKAGE_VERSION)-build-epoch.txt
 
 # Build the HTML and Markdown documentation from the package's source.
+DOCS_SOURCE := $(shell find docs/source -type f -name '*.rst')
 .PHONY: docs docs-html docs-md
 docs: docs-html docs-md
 docs-html: docs/_build/html/index.html
-docs/_build/html/index.html: check test
+docs/_build/html/index.html: $(DOCS_SOURCE) check test
 	if [ ! -d docs/source/_static ]; then \
 	  mkdir docs/source/_static/; \
 	fi