DOC: Help for Makefile.

Makefile

@@ -21,7 +21,7 @@
 
 # Just a collection of scripts
 
-.PHONY: all autopep8 test
+.PHONY: all autopep8 test help
 
 # Do the integration tests.
 # Accepts freestyle arguments like so:
@@ -29,9 +29,26 @@
 test:
 	cd tests &&	pytest $(test_opts)
 
+
+# Just print the help.
+define HELP
+The most common targets:
+
+make test :: Do the integration tests.  Accepts freestyle arguments like so:
+             `make test test_opts=test_foo.py -k test_function`
+Prepare everything for running.
+make autopep8 :: Autoformatting for all tests
+make all :: Run autopep8 and test
+endef
+export HELP
+help:
+	@echo "$$HELP"
+
+
 # Run the tests through autopep8.
 autopep8:
 	autopep8 -ri tests
 
+
 # Meta target to call the other targets.
 all: autopep8 test