[doc] Add CONTRIBUTING.md

Change-Id: Ic2554acbfb1d9de63e5b0b40de833f114bfa3108
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>

CONTRIBUTING.md

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+# Contributing to Eclipse GMF Runtime
+
+Thanks for your interest in this project.
+
+## Project description
+
+The code in this repository contains the GMF Notation metamodel, which is part of the Eclipse GMF Runtime project.
+
+The Eclipse GMF Runtime is an industry proven application framework for creating graphical editors
+using Eclipse EMF and Eclipse GEF.
+
+The GMF Runtime provides many features that one would have to code by hand if using EMF and GMF directly.
+
+- A set of reusable components for graphical editors, such as printing, image export, actions and toolbars and much more.
+- A standardized model to describe diagram elements, which separates between the semantic (domain) and notation (diagram) elements.
+- A command infrastructure that bridges the different command frameworks used by EMF and GEF.
+- An extensible framework that allows graphical editors to be open and extendible.
+
+- https://projects.eclipse.org/projects/modeling.gmf-runtime
+
+## Developer resources
+
+Information regarding source code management, builds, coding standards, and
+more.
+
+- https://projects.eclipse.org/projects/modeling.gmf-runtime/developer
+
+The project maintains the following source code repositories
+
+- https://git.eclipse.org/r/plugins/gitiles/gmf-notation/org.eclipse.gmf.notation
+- https://git.eclipse.org/r/plugins/gitiles/gmf-runtime/org.eclipse.gmf-runtime
+
+This project uses Bugzilla to track ongoing development and issues.
+
+- Search for issues: https://bugs.eclipse.org/bugs/buglist.cgi?product=GMF-Runtime
+- Create a new report: https://bugs.eclipse.org/bugs/enter_bug.cgi?product=GMF-Runtime
+
+Be sure to search for existing bugs before you create another one. Remember that
+contributions are always welcome!
+
+## Eclipse Development Process
+
+This Eclipse Foundation open project is governed by the Eclipse Foundation
+Development Process and operates under the terms of the Eclipse IP Policy.
+
+## Eclipse Contributor Agreement
+
+Before your contribution can be accepted by the project team contributors must
+electronically sign the Eclipse Contributor Agreement (ECA).
+
+- http://www.eclipse.org/legal/ECA.php
+
+Commits that are provided by non-committers must have a Signed-off-by field in
+the footer indicating that the author is aware of the terms by which the
+contribution has been provided to the project. The non-committer must
+additionally have an Eclipse Foundation account and must have a signed Eclipse
+Contributor Agreement (ECA) on file.
+
+For more information, please see the Eclipse Committer Handbook:
+https://www.eclipse.org/projects/handbook/#resources-commit
+
+## Contact
+
+Contact the project developers via the project's "dev" list.
+
+- https://accounts.eclipse.org/mailing-list/gmf-dev