Add readme with reference to run tests

Author: roaffix

arrayfire/array_api/README.md

@@ -0,0 +1,9 @@
+# ArrayFire ArrayAPI
+
+Specification Documentation: [source](https://data-apis.org/array-api/latest/purpose_and_scope.html)
+
+Run tests
+
+```bash
+python -m pytest arrayfire/array_api
+```