Update Readme

Add max_features > n_features test
Add make doc

Makefile

@@ -21,6 +21,9 @@ push:  ## Push code with tags
 test:  ## Run tests
 	python -m unittest -v stree.tests
 
+doc:  ## Update documentation
+	make -C docs --makefile=Makefile html
+
 help: ## Show help message
 	@IFS=$$'\n' ; \
 	help_lines=(`fgrep -h "##" $(MAKEFILE_LIST) | fgrep -v fgrep | sed -e 's/\\$$//' | sed -e 's/##/:/'`); \
@@ -36,4 +39,4 @@ help: ## Show help message
 		printf "%-20s %s" $$help_command ; \
 		printf '\033[0m'; \
 		printf "%s\n" $$help_info; \
-	done
+	done