resolves #71: minor improvements to Makefile

Makefile

@@ -1,12 +1,25 @@
-.PHONY: build py2shell py3shell test
+.PHONY: info build shell py2 py3 test
+
+info:
+	@echo ""
+	@echo "Available Make Commands"
+	@echo ""
+	@echo "build:	builds the image"
+	@echo "py2:	mounts ~/Documents/nd2s to /var/nd2s and runs a Python 2.7 interpreter"
+	@echo "py3:	mounts ~/Documents/nd2s to /var/nd2s and runs a Python 3.4 interpreter"
+	@echo "test:	runs all unit tests (in Python 3.4)"
+	@echo ""
 
 build:
 	docker build -t jimrybarski/nd2reader .
 
-py2shell:
+shell:
+	docker run --rm -v ~/Documents/nd2s:/var/nd2s -it jimrybarski/nd2reader bash
+
+py2:
 	docker run --rm -v ~/Documents/nd2s:/var/nd2s -it jimrybarski/nd2reader python2.7
 
-py3shell:
+py3:
 	docker run --rm -v ~/Documents/nd2s:/var/nd2s -it jimrybarski/nd2reader python3.4
 
 test:	build