add changlog.md and contributing.md (#15)

* add changlog.md and contributing.md

* fix typo, align uppercase and lowercase, adjust some words

Author: Summer

CHANGELOG.md

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+### 1.2.0 (2017-12-22)
+* [Fixed] Users get no hint with building Windows image against Docker Linux container
+* [Added] Add support to scaffold Azure IoT Edge Custom Module in FSharp
+
+### 1.1.0 (2017-12-06)
+* [Fixed] Docker image hint in deployment.json is not clear enough
+
+### 1.0.0 (2017-11-15)
+* [Added] Add support to scaffold Azure IoT Edge Custom Module in CSharp
+* [Added] Add support to scaffold only Azure IoT Edge deployment manifest
+* [Added] Add support to scaffold targeting only linux-x64 or windows-nano architecture
+* [Added] Add ready-to-use Azure IoT Edge Custom Module template

CONTRIBUTING.md

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+## Prerequisites
+* Latest [.NET Core SDK](https://www.microsoft.com/net/download/windows/)
+
+## Setup
+1. Fork and clone the repository
+2. Install the .NET Core SDK
+3. Install the template `dotnet new -i .\content\dotnet-template-azure-iot-edge-module\`
+4. Use the template to scaffold `dotnet new aziotedgemodule -n <your_module_name>`
+
+## Test
+Make sure you have run `dotnet test` before submitting Pull Requests.