add recipe for marshmallow-jsonschema

[k-dominik]

Checklist

• Title of this PR is meaningful: e.g. "Adding my_nifty_package", not "updated meta.yaml".
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• Source is from official source.
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Link @fuhrysteve agreeing to be listed as maintainer: fuhrysteve/marshmallow-jsonschema#153 (comment)

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipes/marshmallow_jsonschema) and found it was in an excellent condition.

[k-dominik]

Dearest @conda-forge/help-python, this PR is ready to roll :)

[dopplershift]

@fuhrysteve can you confirm that you are willing to be a maintainer for this recipe?

[k-dominik]

Hi @dopplershift,

thank you for looking into this!
Link @fuhrysteve agreeing to be listed as maintainer: fuhrysteve/marshmallow-jsonschema#153 (comment)

[dopplershift]

Thanks @k-dominik !