Add instruction to create version.json before running tests

[boolean5]

In a recent change in the README, the step to run make test was replaced by a step to run flake8 and a step to run the unit tests. This way the step that creates the version.json file (present in the Makefile under the test target) is omitted. As a result, most of the tests are failing with
FileNotFoundError: [Errno 2] No such file or directory: 'version.json'.

This can be resolved by simply adding an instruction to run
echo '{"commit":"1","version":test","source":"testing"}' > version.json before executing the command that runs the tests.

I understand from #135 that there is a plan to replace these instructions, so it might not be worth fixing this now. @skim1102, what do you think?