Adding some test prerequisite docs

README.md

@@ -25,12 +25,19 @@ from vipscore_common.data_utils import *
 ### Unit tests
 The tests are located in the `tests` folder, and we're using [Pytest](https://docs.pytest.org/)
 
+Prerequisite: To test, use a venv, install this package in it by running:
+``` bash
+(venv) $ python -m pip install -e .
+```
+
 To run the unit tests, move to the root folder of the project, and execute:
 
 ``` bash
 pytest -v
 ```
 
+
+
 ### Using bumpver
 For developers: When you want to publish a new version, use
 ``` bash