Update installation.mdx to fix typo (#1219)

Author: vince-refiti

markdown-pages/docs/manual/installation.mdx

@@ -56,7 +56,7 @@ bun create rescript-app
 - Trigger a ReScript build:
 
   ```sh
-  npm run build:res
+  npm run res:build
   ```
 - If you selected the "basic" template, simply run it with: