Add note about proxy mode for stdio

Author: danbarr

docs/toolhive/guides-cli/run-mcp-servers.mdx

@@ -159,9 +159,10 @@ server.
 ToolHive supports the following transport methods:
 
 - **Standard I/O** (`stdio`), default:\
-  ToolHive redirects SSE traffic from the client to the container's standard
-  input and output. This acts as a secure proxy, ensuring that the container
-  doesn't have direct access to the network or the host machine.
+  ToolHive redirects SSE or Streamable HTTP traffic from the client to the
+  container's standard input and output. This acts as a secure proxy, ensuring
+  that the container doesn't have direct access to the network or the host
+  machine.
 
 - **HTTP with SSE (server-sent events)** (`sse`):\
   ToolHive creates a reverse proxy that forwards requests to the container using
@@ -179,6 +180,11 @@ the client ecosystem. Once we confirm that ToolHive's supported clients support
 Streamable HTTP, we will make it the default proxy transport method for stdio
 servers.
 
+Currently, you can add the `--proxy-mode streamable-http` flag to the
+[`thv run`](../reference/cli/thv_run.md) command to use Streamable HTTP for
+stdio servers. This will ensure that the server is compatible with the latest
+MCP specification and can be used with clients that support Streamable HTTP.
+
 :::
 
 ### Run a server from a Docker image