Recommend virtualenv instead of pip install --user about openfermion

[babbush]

We actually provide a docker image which is a preconfigured virtual environment essentially. I'd like to hear some other opinions on this one because I am of the opinion that we want to avoid unnecessarily complicated install instructions, especially for those who are avoiding a develop install and are likely to be less sophisticated users. In other words, I think that most people who know how to use virtual environments aren't going to need our install instructions in the first place.

[DanielSank]

we want to avoid unnecessarily complicated install instructions

Agreed. It's unfortunate that virtualenv is still unnecessarily complicated, but I guess that's the reality of life.

especially for those who are avoiding a develop install and are likely to
be less sophisticated users.

So, in that case, why recommend the --user flag in the first place? Is that to avoid having to sudo?

In other words, I think that most people who know how to use virtual environments
aren't going to need our install instructions in the first place.

Well, see issue #38...

[babbush]

Yes, its so they don't need to use sudo (we certainly don't want that). Regarding #38, I think the solution is to (as you say) remind people to first upgrade pip. I will do this on my next pull request sometime this weekend.