Added in the contributing guide.

Author: robertmassaioli

CONTRIBUTING.md

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+# Contributing to json-schema-viewer
+
+Thank you for considering a contribution to json-schema-viewer! Pull requests, issues and comments are welcome. For pull requests, please:
+
+* Add tests for new features and bug fixes
+* Follow the existing style
+* Separate unrelated changes into multiple pull requests
+
+See the existing issues for things to start contributing.
+
+For bigger changes, please make sure you start a discussion first by creating an issue and explaining the intended change.
+
+Atlassian requires contributors to sign a Contributor License Agreement, known as a CLA. This serves as a record stating that the contributor is entitled to contribute the code/documentation/translation to the project and is willing to have it used in distributions and derivative works (or is willing to transfer ownership).
+
+Prior to accepting your contributions we ask that you please follow the appropriate link below to digitally sign the CLA. The Corporate CLA is for those who are contributing as a member of an organization and the individual CLA is for those contributing as an individual.
+
+* [CLA for corporate contributors](https://opensource.atlassian.com/corporate)
+* [CLA for individuals](https://opensource.atlassian.com/individual)