Add file names to .env file examples

Author: jamesopstad

src/content/docs/workers/vite-plugin/reference/cloudflare-environments.mdx

@@ -87,15 +87,11 @@ vars = { MY_VAR = "Production var" }
 
 Next, provide `.env.staging` and `.env.production` files:
 
-```sh
-# .env.staging
-
+```sh title=".env.staging"
 CLOUDFLARE_ENV=staging
 ```
 
-```sh
-# .env.production
-
+```sh title=".env.production"
 CLOUDFLARE_ENV=production
 ```