Documentation clarifications in basic_usage and basic_setup #262

Hi everyone. I'm starting to work with OpenRAM and I think it's a great project. I had a few confusions I'd like to post here in case others got stuck like I did.

I think the directory names have changed, I needed to set OPENRAM_HOME to export OPENRAM_HOME="path/to/OpenRAM/compiler" (the capitalization is off, the info is correct in basic_setup.md however)

Moreover, it wasn't immediately clear to me how to get the python environment working - I think miniconda/anaconda caused more problems than it fixed. Might I suggest also recommending using venv in basic_setup.md as follows?

cd OpenRAM
python3 -m venv .
source bin/activate
python3 -m pip install openram

(as a MacOS/homebrew user, trying to do anything with the local pip3 command ends up being more annoying and I've had better luck with venv versus Anaconda or the system pip).

Another small documentation clarification: to pass arguments into the macros Makefile, one needs to pass, e.g., make OPENRAM_OPTS=-n example_config_scn4m_subm.