.Net: Small fixes for C# tutorial (#3449)

### Motivation and Context

A few small fixes to make it easier for those getting started with C#

### Description

* Fix api name in sample code that has changed
* Make it easier for users to install the right package

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

README.md

@@ -65,7 +65,7 @@ from either OpenAI or Azure OpenAI and to run one of the C#, Python, and Java co
 ### For C#:
 
 1. Create a new console app.
-2. Add the semantic kernel nuget `Microsoft.SemanticKernel`.
+2. Add the semantic kernel nuget [Microsoft.SemanticKernel](https://www.nuget.org/packages/Microsoft.SemanticKernel/).
 3. Copy the code from [here](dotnet/README.md) into the app `Program.cs` file.
 4. Replace the configuration placeholders for API key and other params with your key and settings.
 5. Run with `F5` or `dotnet run`

dotnet/README.md

@@ -26,7 +26,7 @@ using Microsoft.SemanticKernel.Connectors.AI.OpenAI;
 
 var builder = new KernelBuilder();
 
-builder.WithAzureChatCompletionService(
+builder.WithAzureOpenAIChatCompletionService(
          "gpt-35-turbo",                      // Azure OpenAI Deployment Name
          "https://contoso.openai.azure.com/", // Azure OpenAI Endpoint
          "...your Azure OpenAI Key...");      // Azure OpenAI Key