Update installation instructions for FlowForge styles

Added prerequisite note for custom Filament theme setup before including FlowForge styles.

Author: michaelnjuguna

docs/content/1.getting-started/3.installation.md

@@ -26,13 +26,15 @@ composer require relaticle/flowforge
 
 ### Include CSS Assets
 
+Prerequisite: You need a custom Filament theme to include the FlowForge styles.
+
 ::alert{type="warning"}
 If you haven't set up a custom theme for Filament, follow the [Filament Docs](https://filamentphp.com/docs/4.x/styling/overview#creating-a-custom-theme) first.
 ::
 
-Add the plugin's views to your theme CSS file:
+Once you have a custom Filament theme set up, add the plugin's views to your theme CSS file:
 
-```css [resources/css/app.css]
+```css [resources/css/filament/admin/theme.css]
 @source "../../../../vendor/relaticle/flowforge/resources/views/**/*.blade.php";
 ```