document preloading only used material icon variants

Agent-Logs-Url: https://github.com/MudBlazor/MudBlazor.Icons/sessions/9eec0945-aad2-4b3c-95af-58949556483e

Co-authored-by: ScarletKuro <19953225+ScarletKuro@users.noreply.github.com>

Author: Copilot

documentation/material_icons_usage.md

@@ -9,37 +9,23 @@
 | 1.0.0  => |     7.0.0-preview.4 =>      |     .NET 7 & NET 8      |
 
 
-To use the icons in your MudBlazor project while reducing first-load flicker, preload the Material Icons font files before loading the stylesheet:
+To use the icons in your MudBlazor project while reducing first-load flicker, preload only the font variants you use before loading the stylesheet:
 
 ```html
 <link rel="preload"
       href="_content/MudBlazor.FontIcons.MaterialIcons/font/MaterialIcons.woff2"
       as="font"
       type="font/woff2"
       crossorigin>
-<link rel="preload"
-      href="_content/MudBlazor.FontIcons.MaterialIcons/font/MaterialIconsOutlined.woff2"
-      as="font"
-      type="font/woff2"
-      crossorigin>
-<link rel="preload"
-      href="_content/MudBlazor.FontIcons.MaterialIcons/font/MaterialIconsRound.woff2"
-      as="font"
-      type="font/woff2"
-      crossorigin>
-<link rel="preload"
-      href="_content/MudBlazor.FontIcons.MaterialIcons/font/MaterialIconsSharp.woff2"
-      as="font"
-      type="font/woff2"
-      crossorigin>
-<link rel="preload"
-      href="_content/MudBlazor.FontIcons.MaterialIcons/font/MaterialIconsTwoTone.woff2"
-      as="font"
-      type="font/woff2"
-      crossorigin>
 <link href="_content/MudBlazor.FontIcons.MaterialIcons/css/font.min.css" rel="stylesheet" />
 ```
 
+Other available variants that can be preloaded as needed:
+- `_content/MudBlazor.FontIcons.MaterialIcons/font/MaterialIconsOutlined.woff2`
+- `_content/MudBlazor.FontIcons.MaterialIcons/font/MaterialIconsRound.woff2`
+- `_content/MudBlazor.FontIcons.MaterialIcons/font/MaterialIconsSharp.woff2`
+- `_content/MudBlazor.FontIcons.MaterialIcons/font/MaterialIconsTwoTone.woff2`
+
 Alternatively, you can use the following CDN links:
 
 ```html