Running make install before checking out submodules requires make clean

[snissn]

Follow up issue from #26

I was testing and ran into an edge case.

• When I first ran make install I did not check out the submodules - git submodule init; git submodule update;
• Running make install runs make .env which uses the existance of the file .env in the project directory as a criteria to run
• Since the submodules didn't exist the .env files for test-fevm-hardhat were not properly created.

I feel that this is a fairly easy situation to occur during set up and can create a very confusing debugging process for the user/developer. I want to document this here. I think there are also a few good and easy to implement solutions:

1. include a note in the Readme to run git submodule init; git submodule update; in order to download the external testing libraries. Also a note that make clean && make install can clean any config options. I think this would be really helpful and awesome to avoid future concerns
2. add git submodule init; git submodule update; to make install. I'm ok with this solution but I think that it's a bit messy to run it in "install" and the Readme solution is more straightforward