[MINOR] Temp skip nb builds, improve docs.

Author: Mark2000

docs/Makefile

@@ -20,11 +20,8 @@ help:
 	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
 
 clean:
-	cp build/doctrees/nbsphinx/README.txt _tmp_README.txt
 	rm -rf "source/examples" "source/api_reference" "build"
 	mkdir -p "build/doctrees/nbsphinx"
-	cp _tmp_README.txt build/doctrees/nbsphinx/README.txt
-	rm _tmp_README.txt
 
 view:
 	# works on macOS