Create CONTRIBUTING.md

Author: jasonjoh

CONTRIBUTING.md

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+# Contributing to Microsoft Graph training repositories
+
+Thank you for contributing to this project! Before submitting your pull request, be sure to consider the following.
+
+## Overview
+
+The code in this repository serves three purposes:
+
+- The Markdown files in the [tutorial](/tutorial) folder are published as a tutorial on the [Microsoft Graph tutorials](https://docs.microsoft.com/graph/tutorials) page.
+- The sample project in the [demo](/demo) folder is the source for a [Microsoft Graph quick start](https://developer.microsoft.com/graph/quick-start).**\***
+- The sample project in the demo folder is also downloadable directly from GitHub and should run as-is after some simple configuration.
+
+> **\*** Not all training repositories are available as quick starts (yet).
+
+This is important to keep in mind, because changes in one place *may* require changes in another, to keep things in sync. Whereever possible, the Markdown files refer to the source code files directly (using a custom `:::code` syntax), so that updating code in source will automatically update the code in Markdown.
+
+## Updating code
+
+The `:::code` syntax used in Markdown depends on specific comments in the source code file. These comments look like the following:
+
+```csharp
+// <MySnippet>
+Console.WriteLine("Hello World!");
+// </MySnippet>
+```
+
+If you update code between these "marker" comments, the Markdown files will automatically get those changes when published to the Microsoft Graph documentation site. If you update code outside of those comments, it's very likely that you'll need to update the corresponding Markdown.
+
+## Adding features
+
+While the enthusiasm is appreciated, please don't send pull requests to add new features to the sample. Because this repository is primarily a "build your first app" tutorial, the feature set is limited, by design.
+
+## Submitting pull requests
+
+Please submit all pull requests to the `master` branch.
+
+## When do changes get published?
+
+Publishing of updates to the [Microsoft Graph tutorials](https://docs.microsoft.com/graph/tutorials) site is not automatic. Changes must first be promoted to the `live` branch, then a build must be triggered by the site admins. This is typically done on an "as-needed" basis.
+
+## Code of conduct
+
+This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/). For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or contact [[email protected]](mailto:[email protected]) with any additional questions or comments.