Fix badges in README.rst

[epassaro]

Description

• Replaced coverage badge with codecov.
• Update zenodo badge and bibtex citation.
• Moved badges to the top.

Motivation and Context

Badges should stay at the top of README.

How Has This Been Tested?

Just check rendered README at PR tree.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have assigned/requested two reviewers for this pull request.

[codecov]

Codecov Report

Merging #1195 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1195   +/-   ##
=======================================
  Coverage   77.13%   77.13%           
=======================================
  Files          89       89           
  Lines        5551     5551           
=======================================
  Hits         4282     4282           
  Misses       1269     1269           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d9e1831...17213bd. Read the comment docs.