Update files from fatiando/contributing

[fatiando-bot]

Changes have been made in https://github.com/fatiando/contributing to: AUTHORSHIP.md CONTRIBUTING.md MAINTENANCE.md Update the copies in this repository to match. See https://github.com/fatiando/contributing/commit/998715c4f79d194cc682b996775863a8f4541ba7

[welcome[bot]]

💖 Thanks for opening this pull request! 💖

Please make sure you read our Contributing Guide and abide by our Code of Conduct.

A few things to keep in mind:

• Remember to run make format to make sure your code follows our style guide.
• If you need help writing tests, take a look at the existing ones for inspiration. If you don't know where to start, let us know and we'll walk you through it.
• All new features should be documented. It helps to write the docstrings for your functions/classes before writing the code. This will help you think about your code design and results in better code.
• No matter what, we are really grateful that you put in the effort to do this! ⭐

[codecov[bot]]

Codecov Report

Merging #5 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master       #5   +/-   ##
=======================================
  Coverage   65.82%   65.82%           
=======================================
  Files           3        3           
  Lines          79       79           
  Branches       11       11           
=======================================
  Hits           52       52           
  Misses         27       27

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