README.md updated

Author: dotarj

README.md

@@ -4,4 +4,59 @@
 [![nuget](https://img.shields.io/nuget/v/PartialResponse.AspNetCore.Mvc.Formatters.Json.svg)](https://www.nuget.org/packages/PartialResponse.AspNetCore.Mvc.Formatters.Json)
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+
+PartialResponse.AspNetCore.Mvc.Formatters.Json provides JSON partial response support for ASP.NET Core MVC. This package is also [available for ASP.NET Web API](https://www.nuget.org/packages/WebApi.PartialResponse/).
+
+## Getting started
+
+First, add a dependency to PartialResponse.AspNetCore.Mvc.Formatters.Json using the NuGet package manager or by adding a package reference to the .csproj:
+
+```xml
+<ItemGroup>
+  <PackageReference Include="PartialResponse.AspNetCore.Mvc.Formatters.Json" Version="x.x.x" />
+</ItemGroup>
+```
+
+Then, remove the `JsonOutputFormatter` from the output formatters and add the `PartialJsonOutputFormatter`:
+
+```csharp
+public void ConfigureServices(IServiceCollection services)
+{
+    services
+        .AddMvc(options => options.OutputFormatters.RemoveType<JsonOutputFormatter>())
+        .AddPartialJsonFormatters();
+}
+```
+
+The `fields` parameter value, which is used to filter the API response, is case-sensitive by default, but this can be changed using the `MvcPartialJsonOptions`:
+
+```csharp
+public void ConfigureServices(IServiceCollection services)
+{
+    services.Configure<MvcPartialJsonOptions>(options => options.IgnoreCase = true);
+}
+```
+
+That's it!
+
+## Understanding the fields parameter
+
+The `fields` parameter filters the API response so that the response only includes a specific set of fields. The `fields` parameter lets you remove nested properties from an API response and thereby reduce your bandwidth usage.
+
+The following rules explain the supported syntax for the `fields` parameter value, which is loosely based on XPath syntax:
+
+* Use a comma-separated list (`fields=a,b`) to select multiple fields.
+* Use an asterisk (`fields=*`) as a wildcard to identify all fields.
+* Use parentheses (`fields=a(b,c)`) to specify a group of nested properties that will be included in the API response.
+* Use a forward slash (`fields=a/b`) to identify a nested property.
+
+In practice, these rules often allow several different `fields` parameter values to retrieve the same API response. For example, if you want to retrieve the playlist item ID, title, and position for every item in a playlist, you could use any of the following values:
+
+* `fields=items/id,playlistItems/snippet/title,playlistItems/snippet/position`
+* `fields=items(id,snippet/title,snippet/position)`
+* `fields=items(id,snippet(title,position))`
+
+**Note:** As with all query parameter values, the fields parameter value must be URL encoded. For better readability, the examples in this document omit the encoding.
+
+**Note:** Due to the relatively slow performance of LINQ to JSON (Json.NET), the usage of PartialJsonOutputFormatter has a performance impact compared to the regular Json.NET serializer. Because of the reduced traffic, the overhead in time could be neglected.