adding contribution instructions (closes #89)

[djarecka]

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 change)

Summary

• adding CONTRIBUTING.md
• adding zenodo file

I've created manually a first zenodo file (I haven't uploaded anything to zenodo, just the file for now), please check your info.
(@satra - I assumed that you want me the last; @mgxd - I've changed your affiliation to Stanford, in Nipype you still have MIT; @kaczmarj - I left MIT)

Checklist

• All tests passing
• I have added tests to cover my changes
• I have updated documentation (if necessary)
• My code follows the code style of this project
  (we are using black: you can pip install pre-commit,
  run pre-commit install in the pydra directory
  and black will be run automatically with each commit)

Acknowledgment

• I acknowledge that this contribution will be available under the Apache 2 license.

[codecov]

Codecov Report

Merging #193 into master will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #193   +/-   ##
=======================================
  Coverage   86.33%   86.33%           
=======================================
  Files          17       17           
  Lines        2758     2752    -6     
  Branches      729      726    -3     
=======================================
- Hits         2381     2376    -5     
+ Misses        243      241    -2     
- Partials      134      135    +1     

Flag	Coverage Δ
#unittests	83.61% <ø> (-2.72%)	⬇️

Impacted Files	Coverage Δ
pydra/engine/workers.py	84.00% <0.00%> (ø)	⬆️
pydra/engine/submitter.py	91.34% <0.00%> (ø)	⬆️
pydra/__init__.py	68.75% <0.00%> (ø)	⬆️
pydra/engine/helpers.py	85.79% <0.00%> (ø)	⬆️
pydra/engine/specs.py	91.63% <0.00%> (+0.17%)	⬆️

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[mgxd]

looks good - I've updated Chris's and my affiliations, and some missed Pydra substitutions