update local test readme

Author: dnth

tests/README.md

@@ -2,8 +2,8 @@
 
 To run the tests first install `pytest`:
 
-```pip install pytest pytest-cov```
+```pip install pytest```
 
 Then `cd` into the fastdup repo root directory and run:
 
-```pytest --cov=fastdup```
+```pytest```