Development: Improve sandbox documentation for non-conda users

CONTRIBUTING.md

@@ -8,3 +8,9 @@ Creating the streamz conda environment can be achieved by simply running ```cond
 
 ### Using Conda Environment
 The streamz conda environment can be activated by running ```conda activate streamz_dev```
+
+### Run Software Tests
+```shell
+pip install --editable=. --requirement=requirements-test.txt
+pytest -vvv
+```

requirements-test.txt

@@ -0,0 +1,11 @@
+# That's a minimal set of packages to satisfy ~1000 test cases
+# of the whole test suite. See also `./ci/*.yml` for full conda
+# environment descriptions.
+
+dask[array,distributed]
+flaky
+ipywidgets
+pandas
+pyarrow
+pytest<9
+requests