[DOC] Add Python version info

[tsalo]

Closes #124.

Changes proposed in this pull request:

• Specify minimum Python version in README.
• Add Python version badges tied to PyPi to README and docs index page.
• Make duecredit’s import warning sound more like a warning and less
  like an error.

[codecov]

Codecov Report

Merging #126 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #126   +/-   ##
=======================================
  Coverage   49.68%   49.68%           
=======================================
  Files          32       32           
  Lines        2037     2037           
=======================================
  Hits         1012     1012           
  Misses       1025     1025

Impacted Files	Coverage Δ
tedana/info.py	100% <ø> (ø)	⬆️
tedana/due.py	50% <ø> (ø)	⬆️

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[KirstieJane]

I think this looks great @tsalo! Thank you!!

Might be best to let someone else who knows the codebase better take a look before merging (even though I've approved the PR) but from a documentation point of view I think this is great!

[tsalo]

@KirstieJane Thank you for reviewing! I'll wait until @emdupre has a chance to review the code itself (not that much is changed), but I think that the documentation is the most important aspect so I'm very glad that the result is readable.

[emdupre]

Thanks so much @tsalo ! I actually don't know if it works 3.7, too, now, but I'd imagine so !

Depending on how you feel about the need to check that, I have one suggestion: Can we have the badge and the README text match (i.e., either change to say "3.6, 3.7" in the badge or "= 3.6" in the text) ?

[tsalo]

I think it makes the most sense to include 3.7 in the Travis CI. I can do that in this PR.

I don't know if PyPi automatically detects supported Python versions from CI or something, or if you have to manually specify, but you might have to change tedana's PyPi settings to support 3.7. That should update the badge.

[emdupre]

Thanks ! Happy to see it passes with 3.7 😄 I think you need to change this line to update it on PyPi (for the next release). As always, fmriprep has a good example here !

[tsalo]

Awesome. Done. Thanks for finding that!

[emdupre]

Thanks for adding it in ! This LGTM -- merging 🎉