Update the tests readme to be accurate.

Author: gsnedders

html5lib/tests/README

@@ -1,5 +1 @@
-Each testcase file can be run directly through a python interpreter
-(e.g. python test_tokenizer.py).
-
-Some testcases depend on the json module (available since Python 2.6),
-but will fall back to using simplejson if json is not available.
+Each testcase file can be run through nose (using ``nosetests``).