Add dockerfile to languages for discoverability (dotnet#4461)

* Added dockerfile as a lang for discoverability.

* Remove extendedZipContent, as I'm not sure it is needed

* Update README.md

* Update README.md

* Update README.md

github-actions/DotNet.GitHubAction/README.md

@@ -1,6 +1,7 @@
 ---
 languages:
 - csharp
+- dockerfile
 products:
 - dotnet
 - github
@@ -12,11 +13,11 @@ description: "A .NET 5 console application that contains the example from Create
 
 # Create a GitHub Action with .NET
 
-This sample is a console application written in C# from the [Create a GitHub Action with .NETtutorial](https://docs.microsoft.com/dotnet/devops/create-dotnet-github-action). The article gives an overview of what is required to create a .NET GitHub action.
+This sample is a console application written in C# from the [Create a GitHub Action with .NET tutorial](https://docs.microsoft.com/dotnet/devops/create-dotnet-github-action). The article gives an overview of what is required to create a .NET GitHub Action.
 
 ## Sample prerequisites
 
-This sample is written in C# and targets .NET 5. It requires the [.NET 5.0 SDK](https://dotnet.microsoft.com/download/dotnet/5.0).
+This sample is written in C# and targets .NET 5. It requires the [.NET 5.0 SDK](https://dotnet.microsoft.com/download/dotnet/5.0) or later.
 
 ## Building the sample