Suggested updates to README

[arfon]

👋 @lwasser - this PR does two things:

1. Updates the preferred citation for the package to link to the JOSS paper.
2. Removes the Zenodo DOI badge - rationale that this is likely to cause confusion to users, especially if you want to encourage citation of the paper rather than a Zenodo DOI?

[lwasser]

👋 @arfon awesome - thank you for this. i'll merge once CI is happy. Much appreciated. i was actually just going to ping you on the two sets of DOI's. Orcid already has registered the JOSS citation so that is preferred on my end!! many thanks for walking me through this process.

Also Whedon is absolutely awesome. what a friendly bot that walked me through the review process. i'd love to touch base with you at some point on using whedon again for pyopensci. just to revisit that idea! whedon should get funding to support open source review processes in general as you had alluded to!!

[codecov-io]

Codecov Report

Merging #456 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #456   +/-   ##
=====================================
  Coverage      95%    95%           
=====================================
  Files          25     25           
  Lines        1660   1660           
=====================================
  Hits         1577   1577           
  Misses         83     83

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[arfon]

Also Whedon is absolutely awesome. what a friendly bot that walked me through the review process. i'd love to touch base with you at some point on using whedon again for pyopensci. just to revisit that idea! whedon should get funding to support open source review processes in general as you had alluded to!!

Definitely, would love to!

[lwasser]

thank you @arfon merging now!!