docs: Make homepage installation instructions match docs (#2596)

The /docs/installation pages contain this command:

```
npx panda init --postcss
```

But try-panda.tsx, rendered on the homepage, instructs:

```
npm run panda init -p
```

This change makes the homepage match the docs pages.

website/src/components/sections/try-panda.tsx

@@ -11,7 +11,7 @@ const installSteps = [
   },
   {
     title: 'Run the initialize command',
-    command: 'npm run panda init -p'
+    command: 'npx panda init --postcss'
   },
   {
     title: 'Start using Panda in your project',