Update development requirements in README (#3055)

* update requirements

* update

---------

Co-authored-by: catalinaperalta <caperal@microsoft.com>
Co-authored-by: msyyc <70930885+msyyc@users.noreply.github.com>
Co-authored-by: Yuchao Yan <yuchaoyan@microsoft.com>

Author: 3 people

.chronus/changes/update-reqs-2025-2-18-11-17-24.md

@@ -0,0 +1,7 @@
+---
+changeKind: internal
+packages:
+  - "@azure-tools/typespec-python"
+---
+
+Require node version 20.x

README.md

@@ -2,8 +2,9 @@
 
 ## Requirements
 
-- Node 16+
-- Python 3.7+
+-   Node 20+
+-   pnpm 9+
+-   Python 3.8+
 
 ## Develop
 

packages/typespec-python/package.json

@@ -24,7 +24,7 @@
   },
   "tspMain": "dist/src/index.js",
   "engines": {
-    "node": ">=14.0.0"
+    "node": ">=20.0.0"
   },
   "scripts": {
     "clean": "rimraf ./dist ./temp ./venv ./node_modules",