Add contribution.txt file

[Sagar2366]

MindsDB is an Open Sorce project. So please add some contribution related documentation to help others to start contributing in this project.

[mariorodeghiero]

If MindsDB and @torrmal agree? I can create CONTRIBUTING.md, CHANGELOG.md and improvements in the documentation, also start to translate for Portuguese Brazil.

[torrmal]

Hi Mario Yes that will be awesome! Please let me know if you have any questions, feel free to email to Jorge at MindsDB dot com

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On Tue, Feb 26, 2019 at 9:06 AM Mário Antônio do Amaral Rodeghiero < ***@***.***> wrote: If MindsDB and @torrmal <https://github.com/torrmal> agree? I can create CONTRIBUTING.md, CHANGELOG.md and improvements in the documentation, also start to translate for Portuguese Brazil. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#95 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AFoBChRIZkXP80y3Vdo8J766G_9rLZKYks5vRT9ZgaJpZM4bPCWt> .

[mariorodeghiero]

Right Jorge, I'll start contributing and we'll talk by email.

[mariorodeghiero]

@torrmal After merge from my PR to v.1.0, you can already close this issue.

[George3d6]

Added this information in the readme in #281