Adds CONTRIBUTING.md and pull request template (#183)

Links out to Embrace CLA form

.github/CONTRIBUTING.md

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+Contributing
+============
+
+## Contributing License Agreement
+
+Before code can be accepted all contributors must complete our [Individual Contributor License Agreement (CLA)](https://forms.gle/SjXadmUcVwh6NrU68).
+
+## Pull Requests
+
+If you would like to contribute code you can do so through GitHub by
+forking the repository and sending a pull request.
+
+When submitting code, please make every effort to follow existing conventions
+and style in order to keep the code as readable as possible.
+
+Please also run and fix `swiftlint` by using:
+```sh
+$ swift run swiftlint --fix
+```
+
+## Reporting issues
+
+If you have any trouble to start contributing, please [contact us directly](mailto:support@embrace.io) or reach out in our [Community Slack](https://embraceio-community.slack.com/)
+Finally, feel free to open a [new issue](https://github.com/embrace-io/embrace-apple-sdk/issues/new).
+
+

.github/PULL_REQUEST_TEMPLATE.md

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+## Checklist
+
+- [ ] PR Description to summarize changes
+- [ ] Add sufficient test coverage
+- [ ] Read [Contributing Guidelines](./CONTRIBUTING.md)
+- [ ] Agree to [Embrace CLA](https://docs.google.com/forms/d/e/1FAIpQLSct_OV9j5-yGCXkhMKOUKpwTxFWdwCQYTPeESk39lOM6k3uKA/viewform)