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

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

@@ -0,0 +1,33 @@
+# Cosmos client with Azure Function
+
+THis sample demonstrates how to maintain a Cosmos client and reuse the instance among Azure Function executions.
+
+## Prerequisites
+
+- Azure Cosmos DB NoSQL Account
+  - Create a DataBase and Container
+
+## Run
+
+Before running the application you need fill out `EndPointUrl` and `AuthorizationKey` params in the [AppSettings.json](AppSettings.json)
+
+```PowerShell
+dotnet run
+```
+
+## Getting Started
+
+### Create Database and Container
+
+### Send post request
+
+```bash
+curl --location 'http://localhost:7071/api/CosmosClient' \
+--header 'Content-Type: application/json' \
+--data '{
+    "id": "id",
+    "name" : "name",
+    "description" : "description",
+    "isComplete": false
+}'
+```