Update README.md (#6506)

Was unable to get this to work without changing HumanInputMode.ALWAYS
for Azure OpenAI model IDE would not compile


## Why are these changes needed?

Unable to compile until changing

## Related issue number


## Checks

- [x] I've included any doc changes needed for
<https://microsoft.github.io/autogen/>. See
<https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md> to
build and test documentation locally.
- [x] I've added tests (if relevant) corresponding to the changes
introduced in this PR.
- [x] I've made sure all auto checks have passed.

dotnet/README.md

@@ -40,7 +40,7 @@ var assistantAgent = new AssistantAgent(
 // set human input mode to ALWAYS so that user always provide input
 var userProxyAgent = new UserProxyAgent(
     name: "user",
-    humanInputMode: ConversableAgent.HumanInputMode.ALWAYS)
+    humanInputMode: HumanInputMode.ALWAYS)
     .RegisterPrintMessage();
 
 // start the conversation