docs: add trailing slash to /mcp endpoint URLs

The /mcp endpoint requires a trailing slash because the MCP server
is mounted as a sub-application using app.mount(). Starlette's mount
behavior causes a 307 redirect from /mcp to /mcp/, which many MCP
clients fail to handle.

Updates documentation examples to use /mcp/ consistently.

README.md

@@ -203,7 +203,7 @@ curl -X POST 'http://0.0.0.0:4000/v1/chat/completions' \
 {
   "mcpServers": {
     "LiteLLM": {
-      "url": "http://localhost:4000/mcp",
+      "url": "http://localhost:4000/mcp/",
       "headers": {
         "x-litellm-api-key": "Bearer sk-1234"
       }

docs/my-website/docs/mcp.md

@@ -632,7 +632,7 @@ import asyncio
 config = {
     "mcpServers": {
         "mcp_group": {
-            "url": "http://localhost:4000/mcp",
+            "url": "http://localhost:4000/mcp/",
             "headers": {
                 "x-mcp-servers": "dev_group", # assume this gives access to github, zapier and deepwiki
                 "x-litellm-api-key": "Bearer sk-1234",