added portkey to list.md

[hdharish01]

Thanks for contributing to the Hacktoberfest Swag List 😃 🎉! Before submitting your pull request, please check off as many of the items below as you can:

fixes #951 (Add Portkey to the Hacktoberfest Swag List)

1. I have read the Contributing.md file and formatted this PR correctly
2. I'm not adding a company from the blocklist
3. I make sure to fix things promptly if an error or suggestion comes up

Thanks and Happy Hacktoberfest! 🎉
Tagging @crweiner to take a look. 👀

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[vimode]

Thank you for your contribution, I have made some suggestions for better readability.

[codeclimate]

Code Climate has analyzed commit 0c64d9c and detected 0 issues on this pull request.

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[crweiner]

Thank you very much for the PR @hdharish01 and for the assist, @vimode! Let's get Portkey added to the Swag List. 🎉