Keeping version information in table.md.

[swolebro]

In #7, I added some version information to table.md, which could be useful later.

Is there any sane way to add this automatically in report_to_table.py? I pulled the versions by doing a bash loop over all the envs, source activating, calling python -V and pip list, and scanning over the output**. Putting a bunch of subprocess calls in the script is probably going to provide more headache than benefit though. May as well just do it manually by that point.

Is there any way to extract version info from a virtualenv without actually being in it? I guess we could os.walk() and get extract it from the directory names under site-packages, but that's arguably worse than subprocessing bash.

** Incidentally it looked like a handful of environments had broken pips after running all the nox sessions, but I got to look into that more later.

[theacodes]

@swolebro since the nox envs all install latest setuptools and pip, it's probably okay to just spit out the latest version numbers into the table.