[Internal] Usage: Add README.md for usage samples

Microsoft.Azure.Cosmos.Samples/Usage/ApplicationInsights/README.md

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+# Integrate ApplicationInsights with Cosmos DB
+
+This project provides a demo showcasing the usage of the integrating ApplicationInsights with Cosmos DB. The goal is to trace requests.
+
+## Prerequisites
+
+- Azure Cosmos DB NoSQL Account
+  - Create a DataBase and Container
+- Azure ApplicationInsights Account
+  - Create a Azure ApplicationInsights account
+
+## Run
+
+Before running the application you need fill out `CosmosDBEndPointUrl`, `CosmosDBAuthorizationKey` and `ApplicationInsightsConnectionString` params in the [AppSettings.json](AppSettings.json)
+
+```PowerShell
+dotnet run
+```
+
+## Getting Started
+
+### Configure Application Insights Telemetry
+
+```C#
+// <SetUpApplicationInsights>
+IServiceCollection services = new ServiceCollection();
+services.AddApplicationInsightsTelemetryWorkerService((ApplicationInsightsServiceOptions options) => options.ConnectionString = aiConnectionString);
+
+IServiceProvider serviceProvider = services.BuildServiceProvider();
+_telemetryClient = serviceProvider.GetRequiredService<TelemetryClient>();
+// </SetUpApplicationInsights>
+```
+
+### Prepare Client, Database and Container
+
+```C#
+using (CosmosClient client = new CosmosClient(endpoint, authKey, options))
+{
+    Console.WriteLine($"Getting container reference for {containerName}.");
+
+    ContainerProperties properties = new ContainerProperties(containerName, partitionKeyPath: "/id");
+
+    await client.CreateDatabaseIfNotExistsAsync(databaseName);
+    Container container = await client.GetDatabase(databaseName).CreateContainerIfNotExistsAsync(properties);
+
+    await Program.RunCrudDemo(container);
+}
+```
+
+### Flush telemetry data
+
+```C#
+_telemetryClient?.Flush();
+```
+
+### Check captured telemetry in Application Insights
+
+![Alt text](image.png)