Added README for LSP sample

New_Extensibility_Model/Samples/RustLanguageServerProvider/README.md

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+---
+title: Rust Language Server Provider Sample Reference
+description: Language server provider that runs the rust analyzer when a matching document is opened. 
+date: 2023-10-31
+---
+
+# Walkthrough: Rust Language Server Provider Sample
+
+This sample creates a Rust Language Server Provider extension that serves intellisense and tooltips when a rust file is opened in Visual Studio.
+
+## Prerequisites
+This sample requires installing [Rust](https://www.rust-lang.org/tools/install)  and [rust-analyzer.exe](https://github.com/rust-lang/rust-analyzer) found under releases named "rust-analyzer-x86_64-pc-windows-msvc.zip"
+
+## Language Server Provider definition
+
+The extension contains a code file that defines a language server provider and its properties starting with the `VisualStudioContribution` class attribute which makes the server available to Visual Studio:
+
+```csharp
+	[VisualStudioContribution]
+	internal class RustLanguageServerProvider : LanguageServerProvider
+	{
+```
+
+The `LanguageServerProviderConfiguration` property defines information about the server that is available to Visual Studio even before the extension is loaded:
+
+```csharp
+	public override LanguageServerProviderConfiguration LanguageServerProviderConfiguration => new(
+		"%RustLspExtension.RustLanguageServerProvider.DisplayName%",
+		new[] 
+		{ 
+			DocumentFilter.FromDocumentType(RustDocumentType) 
+		});
+```
+
+This configuration object allows setting the display name for the server and specifying one or more document filters. You can also specify a localized string as a display name from [string-resoures.json](./.vsextension/string-resources.json):
+
+```json
+{
+	"RustLspExtension.RustLanguageServerProvider.DisplayName": "Rust Analyzer LSP server"
+}
+```
+
+## Activating the Language Server
+
+Once a document that has a matching document type is opened, Visual Studio calls into `CreateServerConnectionAsync` and requests an `IDuplexPipe` that will be used to communicate with the language server. 
+
+In our sample, the rust-analyzer executable is launched and a duplex pipe is used to communicate with the process.
+
+```csharp
+	public override Task<IDuplexPipe?> CreateServerConnectionAsync(CancellationToken cancellationToken)
+	{
+		ProcessStartInfo info = new ProcessStartInfo();
+		info.FileName = Path.Combine(Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location)!, @"rust-analyzer.exe");
+		info.RedirectStandardInput = true;
+		info.RedirectStandardOutput = true;
+		info.UseShellExecute = false;
+		info.CreateNoWindow = true;
+
+		Process process = new Process();
+		process.StartInfo = info;
+
+		if (process.Start())
+		{
+			return Task.FromResult<IDuplexPipe?>(new DuplexPipe(
+				PipeReader.Create(process.StandardOutput.BaseStream),
+				PipeWriter.Create(process.StandardInput.BaseStream)));
+		}
+
+		return Task.FromResult<IDuplexPipe?>(null);
+	}
+```
+
+## Disabling the server
+
+`LanguageServerProvider` contains a public Boolean property `Enabled`, which is set to `true` by default. This property defines if Visual Studio should activate your server when a matching document type is opened. When `Enabled` is set to `False`, all currently running servers will be stopped and no new instances will be activated until re-enabled.
+
+## Capturing and handling activation failures
+
+After `CreateServerConnectionAsync` completes, Visual Studio will attempt to initialize the server via the provided duplex pipe following standard LSP protocol. Once this step is done, `OnServerInitializationResultAsync` is called where `ServerInitializationResult` denotes if the server succeeded or failed to initialize, and if it failed `LanguageServerInitializationFailureInfo` will contain the exception and message provided by the language server.
+
+```csharp
+	public override Task OnServerInitializationResultAsync(ServerInitializationResult serverInitializationResult, LanguageServerInitializationFailureInfo? initializationFailureInfo, CancellationToken cancellationToken)
+	{
+		if (serverInitializationResult == ServerInitializationResult.Failed)
+		{
+			// Log telemetry for failure and disable the server from being activated again.
+			this.Enabled = false;
+		}
+
+		return base.OnServerInitializationResultAsync(serverInitializationResult, initializationFailureInfo, cancellationToken);
+	}
+```
+
+## Usage
+
+Once deployed, the language server will automatically start once an applicable document type is opened.