Create dep doc (#101)

* Created doc for adding dep to initializr

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CREATING-INITIALIZR_DEPENDENCY.md

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+## Creating a 3rdparty Library Dependency
+
+Initializr uses a .NET templating engine called [Stubble](https://github.com/StubbleOrg/Stubble), an implementation of [Mustache](http://mustache.github.com/). 
+
+When adding a new 3rdparty library dependency, the templating allows a lot of flexibility. There are many areas project that can be modified when your dependency has been selected and your project has been generated.
+
+**In order to add your library dependency `PackageReference` you need to update the following `.csproj` and `.json` files:**
+
++ [Mustache.json](#using-mustachejson) - Describe the dependency parameters that the template engine will use to replace
++ [ReplaceMe.csproj](#using-replacemecsproj) - Adding `PackageReference` to `.csproj` file
+
+**Optional files that can be modified:**
+
++ [Startup.cs](#using-startupcs) - Setting your services up to use the dependency
++ [Program.cs](#using-programcs) - Adding the `Using` statements and webhost configuration
+
+**Less typical files that can be modified:**
+
++ Root (/) Directory
+  - [Dockerfile](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/Dockerfile)
+  - [app.config](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/app.config)
+  - [appsettings.json](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/appsettings.json) 
++ Controllers
+  - [ValuesController.cs](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/Controllers/ValuesController.cs)
++ Models
+  - [ErrorViewModel.cs](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/Models/ErrorViewModel.cs)
+  -  [InitializeContext.cs](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/Models/InitializeContext.cs)
+  -  [SampleData.cs](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/Models/SampleData.cs)
+  -  [TestContext.cs](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/Models/TestContext.cs)
++ Properties
+  - [launchSettings.json](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/Properties/launchSettings.json) 
+  
+
+### Using Mustache.json
+The file [mustache.json](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/mustache.json) handles several areas related to the templating:
+
++ Describing the dependency under the `Params` section
++ Grouping of dependencies by using `CalculatedParams`
++ Setting conditional inclusions and exclusions
++ Specifying `Versions` for the dependencies
+
+### Using ReplaceMe.csproj
+The file [ReplaceMe.csproj](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/ReplaceMe.csproj) is used to add the `PackageReference`(s) for the dependency.
+
+>Note: For this explanation we will name our example project `MyFirstProject`.
+
+This file is used to build `MyFirstProject.csproj` based on the selections made in Initializr.
+
+In order to add a new 3rdparty library dependency to the Initializr, this file will need to contain a section to specify what `PackageReference`(s) needs to be added to the `.csproj` file.
+
+For example, when creating an Initializr dependency template for `MySql` as a 3rdparty library you will see the following in the `ReplaceMe.csproj`:
+
+```
+{{#MySql}}
+    <PackageReference Include="MySql.Data" Version="{{MySqlVersion}}" />
+{{/MySql}}
+```
+>Note `MySql` tag is described in `mustache.json` file.
+
+When `MySql` is selected from Initializr, the above snippet will be added to the `MyFirstProject.csproj` as noted below: 
+
+```
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    ...
+  </PropertyGroup>
+
+  <ItemGroup >
+    <!-- MySql Connector PackageReference -->
+    <PackageReference Include="MySql.Data" Version="8.0.16" />
+    <!-- End of MySql PackageReference -->
+
+    <!-- Newtonsoft.Json is added to each project -->
+    <PackageReference Include="Newtonsoft.Json" Version="12.0.2" />
+    <!-- End of Newtonsoft.json PackageReference -->
+    
+    <!-- Steeltoe ConnectorCore is added when any connector is selected -->
+    <PackageReference Include="Steeltoe.CloudFoundry.ConnectorCore"  Version="2.4.3"/>
+    <!-- End of default connector PackageReference -->
+    
+  </ItemGroup>
+</Project>
+```
+### Using Startup.cs
+The file [Startup.cs](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/Startup.cs) is used to generate the Startup.cs file based on the selected dependencies. 
+
+Some options include adding:
+
++ Required `using` statements
++ Services to add to the [IServiceCollection](https://docs.microsoft.com/en-us/dotnet/api/microsoft.extensions.dependencyinjection.iservicecollection)
++ Application configuration to the [IApplicationBuilder](https://docs.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.builder.iapplicationbuilder)
+
+### Using Program.cs
+The file [Program.cs](https://github.com/SteeltoeOSS/Initializr/blob/dev/src/templates/Mustache/3.x/Steeltoe-WebApi/Program.cs) is used configure your `WebHostBuilder` with your selected dependency.
+
+Some options include adding:
+
++ Required `using` statements
++ Configuration to the [WebHostBuilder](https://docs.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.hosting.webhostbuilder)