fix: update node version in readme (#1239)

Author: jairo-bc

README.md

@@ -8,7 +8,7 @@ The BigCommerce server emulator for local theme development.
 ## Install
 
 Note: Stencil requires the Node.js runtime environment,
-versions 16.x, 18.x are supported.
+versions 20.x are supported.
 
 Run `npm install -g @bigcommerce/stencil-cli`.