[general] moving ios and android project under ./platform folder

CONTRIBUTING.md

@@ -0,0 +1,34 @@
+# Contributing
+
+If you have a usage question for a product built on Mapbox GL (such as our iOS or Android SDKs), please visit https://www.mapbox.com/help/.
+
+If you want to contribute code:
+
+1. Please familiarize yourself with the [install process](INSTALL.md).
+
+1. Ensure that existing [pull requests](https://github.com/mapbox/mapbox-gl-native-ios/pulls) and [issues](https://github.com/mapbox/mapbox-gl-native-ios/issues) don’t already cover your contribution or question.
+
+1. Pull requests are gladly accepted. If there are any changes that developers using one of the GL SDKs should be aware of, please update the **master** section of the relevant changelog(s):
+  * [Mapbox Maps SDK for iOS](platform/ios/CHANGELOG.md)
+  * [Mapbox Maps SDK for macOS](platform/macos/CHANGELOG.md)
+
+1. Prefix your commit messages with the platform(s) your changes affect: `[ios]` or `[macos]`.
+
+Please note the special instructions for contributing new source code files, asset files, or user-facing strings to the [iOS SDK](platform/ios/DEVELOPING.md#contributing) or [macOS SDK](platform/macos/DEVELOPING.md#contributing).
+
+### Github issue labels
+
+Our labeling system is:
+
+ * **minimalistic:** Labels’ usefulness are inversely proportional to how many we have.
+ * **objective:** Labels should be objective enough that any two people would agree on a labeling decision.
+ * **useful:** Labels should track state or capture semantic meaning that would otherwise be hard to search for.
+
+We’ve color-coded our labels by facet to make them easier to use:
+
+ * type (blue)
+ * platform (black)
+ * actionable status (red)
+ * non-actionable status (grey)
+ * importance / urgency (green)
+ * topic / project / misc (yellow)