fix: document ProgressMessage

Author: tomgeorge

docs/protocol.md

@@ -402,6 +402,15 @@ interface TextContent {
     text: string;
 }
 
+/**
+ * Progress messages from the LLM. 
+ */
+interface ProgressContent {
+    type: 'progress';
+    state: 'running|finished';
+    text: string;
+}
+
 /**
  * A reason started from the LLM
  *