Add example summary for azure-identity readme.md (#12509)

Author: v-xuto

sdk/identity/azure-identity/README.md

@@ -137,6 +137,15 @@ Configuration is attempted in the above order. For example, if values for a
 client secret and certificate are both present, the client secret will be used.
 
 # Examples
+
+The following examples are provided below:
+
+* [Authenticating with DefaultAzureCredential](#authenticating-with-defaultazurecredential "Authenticating with DefaultAzureCredential")
+* [Authenticating a service principal with a client secret](#authenticating-a-service-principal-with-a-client-secret "Authenticating a service principal with a client secret")
+* [Authenticating a service principal with a certificate](#authenticating-a-service-principal-with-a-certificate "Authenticating a service principal with a certificate")
+* [Chaining credentials](#chaining-credentials "Chaining credentials")
+* [Async credentials](#async-credentials "Async credentials")
+
 ## Authenticating with `DefaultAzureCredential`
 This example demonstrates authenticating the `BlobServiceClient` from the
 [azure-storage-blob][azure_storage_blob] library using