add root make target for creating html version of docs

Author: Derek Schaller

Makefile

@@ -0,0 +1,11 @@
+.PHONY: help
+help:
+	@echo "Please use \`make <target>' where <target> is one of"
+	@grep -E '^\.PHONY: [a-zA-Z_-]+ .*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = "(: |##)"}; {printf "\033[36m%-30s\033[0m %s\n", $$2, $$3}'
+
+.PHONY: docs ## Generate docs
+docs:
+	@cd docs &&\
+	pip install -r requirements.txt &&\
+	make html &&\
+	cd -

README.md

@@ -112,15 +112,8 @@ Tox can only use whatever versions of python are installed on your system. When
 
 The documentation is generated using the excellent [Sphinx](http://www.sphinx-doc.org/) and a custom theme.
 
-The documentation dependencies are installed by running:
+An HTML version of the documentation is produced by running:
 
 ```sh
-cd docs
-pip install -r requirements.txt
-```
-
-Then to produce a HTML version of the documentation:
-
-```sh
-make html
+make docs
 ```