Add CONTRIBUTING.md

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CONTRIBUTING.md

+# Contributing to LibVLCSharp
+
+We'd love for you to contribute to our source code and to make LibVLCSharp even better than it is
+today! Here are the guidelines we'd like you to follow:
+
+ - [Code of Conduct](https://wiki.videolan.org/Code_of_Conduct/)
+ - [Question or Problem?](#question)
+ - [Issues and Bugs](#issue)
+ - [Feature Requests](#feature)
+ - [Submission Guidelines](#submit)
+ - [Coding Rules](#rules)
+
+## <a name="question"></a> Got a Question or Problem?
+
+If you have questions about how to use LibVLCSharp, please direct these to [StackOverflow](https://stackoverflow.com/questions/tagged/libvlcsharp). The project maintainers hang out in this [Gitter](https://gitter.im/libvlcsharp/Lobby) channel.
+
+## <a name="issue"></a> Found an Issue?
+
+If you find a bug in the source code or a mistake in the documentation, you can help us by
+submitting an issue to our [GitLab](https://code.videolan.org/videolan/LibVLCSharp) Repository. Even better you can submit a Pull Request with a fix.
+
+**Please see the [Submission Guidelines](#submit) below.**
+
+## <a name="feature"></a> Want a Feature?
+
+You can request a new feature by submitting an issue to our [GitLab](https://code.videolan.org/videolan/LibVLCSharp) Repository.  If you
+would like to implement a new feature then consider what kind of change it is:
+
+* **Major Changes** that you wish to contribute to the project should be discussed first in [Gitter](https://gitter.im/libvlcsharp/Lobby) so that we can better coordinate our efforts,
+  prevent duplication of work, and help you to craft the change so that it is successfully accepted
+  into the project.
+* **Small Changes** can be crafted and submitted to the [GitLab](https://code.videolan.org/videolan/LibVLCSharp) or [GitHub](https://github.com/videolan/libvlcsharp/pulls) Repository as a Pull
+  Request.
+
+## <a name="submit"></a> Submission Guidelines
+
+### Submitting an Issue
+
+If your issue appears to be a bug, and hasn't been reported, open a new issue. Help us to maximize the effort we can spend fixing issues and adding new features, by not reporting duplicate issues.
+
+Providing the following information will increase the chances of your issue being dealt with
+quickly:
+
+* **Overview of the Issue** - if an error is being thrown a stack trace helps
+* **Motivation for or Use Case** - explain why this is a bug for you
+* **LibVLCSharp/LibVLC Version(s)** - is it a regression?
+* **Operating System** - is this a problem with all platforms or only specific ones?
+* **Reproduce the Error** - provide a example or an unambiguous set of steps.
+* **Related Issues** - has a similar issue been reported before?
+* **Suggest a Fix** - if you can't fix the bug yourself, perhaps you can point to what might be
+  causing the problem (line of code or commit)
+
+**If you get help, help others. Good karma rulez!**
+
+### Submitting a Pull Request
+Before you submit your pull request consider the following guidelines:
+
+* Search [GitLab](https://code.videolan.org/videolan/LibVLCSharp/merge_requests) or [GitHub](https://github.com/videolan/libvlcsharp/pulls) for an open or closed Pull Request
+  that relates to your submission. You don't want to duplicate effort.
+* Make your changes in a new git branch:
+
+    ```shell
+    git checkout -b my-fix-branch develop
+    ```
+
+* Create your patch, **including appropriate test cases**.
+* Follow our [Coding Rules](#rules).
+* Run the test suite, as described below.
+* Commit your changes using a descriptive commit message.
+
+    ```shell
+    git commit -a
+    ```
+  Note: the optional commit `-a` command line option will automatically "add" and "rm" edited files.
+
+* Push your branch to GitHub:
+
+    ```shell
+    git push origin my-fix-branch
+    ```
+
+In GitHub, send a pull request to `libvlcsharp:master`.
+
+If we suggest changes, then:
+
+* Make the required updates.
+* Re-run the test suite to ensure tests are still passing.
+* Commit your changes to your branch (e.g. `my-fix-branch`).
+* Push the changes to your GitHub repository (this will update your Pull Request).
+
+If the PR gets too outdated we may ask you to rebase and force push to update the PR:
+
+```shell
+git rebase master -i
+git push origin my-fix-branch -f
+```
+
+That's it! Thank you for your contribution!
+
+#### After your pull request is merged
+
+After your pull request is merged, you can safely delete your branch and pull the changes
+from the main (upstream) repository:
+
+* Delete the remote branch on GitHub either through the GitHub web UI or your local shell as follows:
+
+    ```shell
+    git push origin --delete my-fix-branch
+    ```
+
+* Check out the master branch:
+
+    ```shell
+    git checkout master -f
+    ```
+
+* Delete the local branch:
+
+    ```shell
+    git branch -D my-fix-branch
+    ```
+
+* Update your master with the latest upstream version:
+
+    ```shell
+    git pull --ff upstream master
+    ```
+## Coding
+
+### Developer Environment
+- Visual Studio 2017 (with latest patches/updates), with the following workloads/components
+    - .NET desktop development workload
+    - Mobile development with .NET workload
+    - .NET Core cross-platform development
+
+### <a name="rules"></a> Coding Rules
+
+To ensure consistency throughout the source code, keep these rules in mind as you are working:
+
+* All features or bug fixes **must be tested** by one or more unit tests (if possible and applicable).
+* All public API methods **must be documented** with XML documentation.