Mention fish_config for UI config

Guides/fish.md

@@ -7,6 +7,12 @@ There is an installation script in this repository at `Install/fish_install`. Th
 
 A customization script is also available : `Install/fish_custom`. This script copy the prompt template.
 
+## Configure from web browser
+
+```sh
+fish_config
+```
+
 ## Colors
 
 ### Set