Add pytest.ini to main directory (aimacode#548)

* Create pytest.ini

* Update CONTRIBUTING.md

Author: antmarakis

CONTRIBUTING.md

@@ -88,7 +88,7 @@ Fetch the aima-data submodule:
     git submodule init
     git submodule update
 
-Then you can run the testsuite from the `tests` directory with:
+Then you can run the testsuite from the `aima-python` or `tests` directory with:
 
     py.test
 

pytest.ini

@@ -0,0 +1,3 @@
+[pytest]
+filterwarnings =
+    ignore::ResourceWarning