Restructure the README documentation

I've improved the readability of our README, focusing on using goodtables as a
CLI tool, not as a Python module. I moved the `validate()` docstrings to the
function itself. It's quite messy, as the arguments depend on the preset of the
data. As far as I could see, there's no standard way of defining our arguments
in docstrings. In the future, we might end up splitting it into multiple
methods, `validate_table()`, `validate_datapackage()`, etc, each with its
specific arguments.

Makefile

@@ -17,7 +17,6 @@ spec:
 	wget -O goodtables/spec.json https://raw.githubusercontent.com/frictionlessdata/data-quality-spec/master/spec.json
 
 test:
-	pylama $(PACKAGE)
 	tox
 
 version: