Add a conda env as option for readers

[volpatto]

Hi, @ageron!

First of all, congratulations for your great book!

I'm trying here to do a very small contributions in this PR, aiming for conda users (just like me). I'm adding an environment.yml with the same setup as requirements.txt. So, the user now can generate the same environment both for virtualenv (with the requirements.txt) and conda (with the new file).

To do so, one can just run:

$ conda env create -f environment.yml

An advantage with this contribution is the enhanced reproducibility. Also, it is easier for the user, since the user doesn't need to care about packages and versions (everything is already configured) A drawback is that when you update requirements.txt, you have to update environment.yml as well, to match packages' versions. Put it simply, both files have to be maintained.

I updated README with instructions. Please, do a double check there!

Thanks and I hope that you appreciate this PR!

[volpatto]

Moreover, the problem mentioned by you in #369 can be solved if you have an environment.yml file in your repo (at least for Binder), I guess. So Binder will build automatically the environment.

[ageron]

Hi @volpatto ,
That's really nice of you, thanks for the contribution! I already added an environment.yml file in the repository for the 2nd edition, but I didn't have time to add one for the 1st edition. Awesome! 👍