Add help command to the Makefile

Closes #2092

Author: mrbazzan

Makefile

@@ -1,39 +1,44 @@
-.PHONY: example test coverage translatable_strings update_translations
+.PHONY: example test coverage translatable_strings update_translations help
+.DEFAULT_GOAL := help
 
-example:
+example:  ## Run the example application
 	python example/manage.py migrate --noinput
 	-DJANGO_SUPERUSER_PASSWORD=p python example/manage.py createsuperuser \
 		--noinput --username="$(USER)" --email="$(USER)@mailinator.com"
 	python example/manage.py runserver
 
-example_test:
+example_test:  ## Run the test suite for example application
 	python example/manage.py test example
 
-test:
+test:  ## Run the test suite
 	DJANGO_SETTINGS_MODULE=tests.settings \
 		python -m django test $${TEST_ARGS:-tests}
 
-test_selenium:
+test_selenium:  ## Run frontend tests written with Selenium
 	DJANGO_SELENIUM_TESTS=true DJANGO_SETTINGS_MODULE=tests.settings \
 		python -m django test $${TEST_ARGS:-tests}
 
-coverage:
+coverage:  ## Enable coverage measurement during tests
 	python --version
 	DJANGO_SETTINGS_MODULE=tests.settings \
 		python -b -W always -m coverage run -m django test -v2 $${TEST_ARGS:-tests}
 	coverage report
 	coverage html
 	coverage xml
 
-translatable_strings:
+translatable_strings:  ## Update the English '.po' file (and push to Transifex)
 	cd debug_toolbar && python -m django makemessages -l en --no-obsolete
 	@echo "Please commit changes and run 'tx push -s' (or wait for Transifex to pick them)"
 
-update_translations:
+update_translations:  ## Download the updated '.po' file
 	tx pull -a --minimum-perc=10
 	cd debug_toolbar && python -m django compilemessages
 
 .PHONY: example/django-debug-toolbar.png
-example/django-debug-toolbar.png: example/screenshot.py
+example/django-debug-toolbar.png: example/screenshot.py  ## Update the screenshot in 'README.rst'
 	python $< --browser firefox --headless -o $@
 	optipng $@
+
+help:  ## Help message for targets
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) \
+		| awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'