add package readme for Nacos.Microsoft.Extensions.ServiceDiscovery

Signed-off-by: catcherwong <[email protected]>

Author: catcherwong

src/Nacos.Microsoft.Extensions.ServiceDiscovery/README.md

@@ -0,0 +1,17 @@
+# nacos-sdk-csharp.Extensions.ServiceDiscovery
+
+nacos-sdk-csharp.Extensions.ServiceDiscovery provides service registration and discovery With Microsoft.Extensions.ServiceDiscovery.
+
+```csharp
+builder.Services.AddServiceDiscovery(o =>
+{
+    o.RefreshPeriod = TimeSpan.FromSeconds(60);
+})
+.AddConfigurationServiceEndpointProvider()
+.AddNacosSrvServiceEndpointProvider();
+```
+
+## Links
+
+* [Documentation](https://nacos-sdk-csharp.readthedocs.io/en/latest/)
+* [nacos-sdk-csharp GitHub](https://github.com/nacos-group/nacos-sdk-csharp)