Make pytest run instruction clear in contribution guide (#981)

Co-authored-by: Mohsin Mumtaz <mohsin.slanglabs.in>
Co-authored-by: Markus Unterwaditzer <[email protected]>

Author: immohsin

CONTRIBUTING.md

@@ -21,7 +21,8 @@ for you. Run `make` or `make help` to list commands.
 Of course you can always run the underlying commands yourself, which is
 particularly useful when wanting to provide arguments to `pytest` to run
 specific tests. If you want to do that, we expect you to know your way around
-Python development, and you can run the following to get started with `pytest`:
+Python development. To get started, clone the SDK repository, cd into it, set
+up a virtualenv and run:
 
     # This is "advanced mode". Use `make help` if you have no clue what's
     # happening here!