[gnome-builder] add CONTRIBUTING.md

[Christian Hergert <chergert src gnome org>]

commit 6a73540b64ede264453b90dded50a1206e97ca85
Author: Christian Hergert <chergert redhat com>
Date:   Sun Dec 13 23:50:33 2015 -0800

    add CONTRIBUTING.md

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+# Contributing to GNOME Builder
+
+We would love for you to contribute to GNOME Builder!
+
+GNOME Builder is a new IDE focusing on the GNOME desktop environment. It is
+primarily written in C, but allows for plugins in C, C++, Python or Vala.
+Additional compiled languages can also be supported, with some work.
+
+Remeber that the GNOME community is largely made up of part-time contributors
+that do this for fun. Be respectful and assume the best of each other.
+
+## Filing a bug
+
+Please file bugs for issues, enhancements, and features on
+[our Bugzilla](https://bugzilla.gnome.org/enter_bug.cgi?product=gnome-builder)
+bug tracker.
+
+To submit a patch, file a bug and attach your patch to the bug.
+Someone will review your patch shortly after doing so.
+
+## Asking for Help
+
+You can often find the other contributors to GNOME Builder on our IRC channel at
+[irc://irc.gimp.net/#gnome-builder](irc://irc.gimp.net/#gnome-builder).
+If you have any questions, we'd be happy to help you.
+
+In particular, if you'd like to start on a new plugin or feature, stop by
+our IRC channel and we'd be happy to get you set off in the right direction.
+
+## Portability
+
+GNOME Builder is primarily focused on **GNU/Linux** with the **GNOME desktop**.
+
+However, we do often accept patches for various BSD-based operating systems
+and alternate desktops. It is important that you can help keep things working
+for your platform, as the Builder team cannot individually test all
+configurations.
+
+## Testing
+
+We use autotools for our build system. It provides support for running unit
+tests with the `make check` command. We run these tests before releasing
+tarballs, so it is important that you check tests and add new tests when it
+makes sense.
+
+## Licensing
+
+Contributions should be licensed under the LGPL-2.1+ or GPL-3. Permissive
+licensed contributions will also be accepted, but we prefer that original
+contributions are either LGPL-2.1+ or GPL-3 licensed.
+
+## Coding Style
+
+Our coding style matches that of Gtk+. We consider the Gtk+ project an
+upstream, and often push features into Gtk+. This might feel unfamiliar
+at first, but it works well.
+
+We use the recent GNU GCC '11 mode, such as -std=gnu11.
+
+```c
+static GtkWidget *
+example_object_get_widget (ExampleObject  *object,
+                           GError        **error)
+{
+  g_return_val_if_fail (EXAMPLE_IS_OBJECT (object), NULL);
+
+  if (object->widget == NULL)
+    {
+      object->widget = g_object_new (GTK_TYPE_LABEL,
+                                     "visible", TRUE,
+                                     NULL);
+    }
+
+  return object->widget;
+}
+```
+
+Please use new-style Object declarations. Unless you intend to subclass the
+object, make the object final.
+
+```c
+#define EXAMPLE_TYPE_OBJECT (example_object_get_type())
+G_DECLARE_FINAL_TYPE (ExampleObject, example_object, EXAMPLE, OBJECT, GObject)
+```
+
+Builder's default C mode matches our style guide.
+
+## Documentation
+
+Most functions should be obvious what they do from the object type, name,
+and parameters. Add additional documentation when it makes sense.
+
+If you find you come across something particularly tricky, or are being clever,
+please add a comment denoting such.
+