added contributing guide, formatted license file

CONTRIBUTING.md

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+# Contributing to RoaringRoster
+
+Thank you for your interest in contributing to RoaringRoster. 🙌
+
+<a name="issue"></a>
+## Report an Issue
+
+If you have found an unknown bug or want to suggest a feature, please open a new issue in the [GitHub issue tracker](https://github.com/roaringroster/webapp/issues).
+
+In case of a bug, please indicate the individual steps to reproduce the bug. What result did you expect and what happened instead? It is also important for us to know with which operating system version and in which browser including version number you observed the problem.
+
+If you have discovered a security vulnerability, please report it to us confidentially via email to [email protected] instead of opening an issue.
+
+<a name="code"></a>
+## Contribute Code
+
+Please start by proposing new features or bugfixes in a [GitHub issue](https://github.com/roaringroster/webapp/issues) to make sure it fits the direction of the project. Assign the issue to yourself and let people know when you start or stop work to avoid duplication or unfinished tasks.
+
+Please note that we ask you to **read and accept our Contributor License Agreement** so we can approve your contribution. You can find more information in the [related section](#cla) below.
+
+Start by forking the repository and make your changes.
+
+After you have opened a pull request with your changes and [accepted the Contributor License Agreement](#cla-how), your code changes will be reviewed for approval. We will merge them on approval. Pease be aware that contributions that do not fit the project will not be approved.
+
+<a name="cla"></a>
+### Contributor License Agreement (CLA)
+
+#### Why anyway?
+
+* We want to keep things open and simple in the future. Maybe we will realize one day that a different open source license fits better for RoaringRoster? Relicensing without CLA is quite complicated.
+* We plan to distribute single, reusable components of RoaringRoster under a more permissive open source license.
+* We want to enable distribution via app stores under their terms and conditions.
+* We wish to reduce legal risks for everyone involved.
+
+#### What is this about?
+
+Please read our [Individual Contributor License Agreement](https://github.com/roaringroster/cla/blob/master/ICLA.md). This is a legally binding document that documents the rights granted by you to us.
+
+A roughly simplified overview:
+
+* You retain all ownership and rights to your contribution.
+* You confirm that you own the copyright to your contribution.
+* You allow us to (sub)license your contribution under any open source license.
+* Patent claims, warranties and damage liability are mutually excluded.
+
+<a name="cla-how"></a>
+#### How is the process?
+
+##### Do you own the copyright for your entire contribution?
+
+1. Start by creating a pull request with your contribution on GitHub.
+1. You will automatically be presented our [Individual Contributor License Agreement](https://github.com/roaringroster/cla/blob/master/ICLA.md). Please read it.
+1. To make this document effective, please sign the agreement by typing "I have read the CLA Document and I hereby sign the CLA" as additional comment to your pull request.
+
+Your signature will be automatically documented with the date and your Github name in a file inside the same repository.
+
+##### Do you own only the copyright for a part of your contribution?
+
+1. Any other author of the contribution should also sign the Contributor License Agreement as described in the previous answer.
+1. Please let us know if you do not own the copyright to your entire contribution, either as a comment in your pull request or by email to [email protected].
+
+##### Are you an employee and have you created your contribution as part of your employment?
+
+Please have your employer approve the [Corporate Contributor License Agreement](https://github.com/roaringroster/cla/blob/master/CCLA.md), which has the same terms as the [Individual Contributor License Agreement](https://github.com/roaringroster/cla/blob/master/ICLA.md), but addresses legal entities such as companies:
+
+1. To make this document effective, a legal representative of your employer needs to print, fill, sign, scan the Corporate CLA and email the signed copy to us at [email protected].
+1. We will do the same and return a copy signed by both parties to your employer.
+1. Additionaly, you as individual contributor need to sign the Individual Contributor License Agreement with your pull request on GitHub as described in the previous two answers.