docs: style customization updated (#106)

* Style customization doc updated

I believe the doc was not up to date regarding the cutomization of logger

* Update README.md

Co-authored-by: Ayman Bagabas <ayman.bagabas@gmail.com>

* Update README.md

Co-authored-by: Ayman Bagabas <ayman.bagabas@gmail.com>

---------

Co-authored-by: Ayman Bagabas <ayman.bagabas@gmail.com>

README.md

@@ -210,18 +210,18 @@ defined at a global level in [styles.go](./styles.go).
 
 ```go
 // Override the default error level style.
-log.ErrorLevelStyle = lipgloss.NewStyle().
-    SetString("ERROR!!").
-    Padding(0, 1, 0, 1).
-    Background(lipgloss.AdaptiveColor{
-        Light: "203",
-        Dark:  "204",
-    }).
-    Foreground(lipgloss.Color("0"))
+styles := log.DefaultStyles()
+styles.Levels[log.ErrorLevel] = lipgloss.NewStyle().
+	SetString("ERROR!!").
+	Padding(0, 1, 0, 1).
+	Background(lipgloss.Color("204")).
+	Foreground(lipgloss.Color("0"))
 // Add a custom style for key `err`
-log.KeyStyles["err"] = lipgloss.NewStyle().Foreground(lipgloss.Color("204"))
-log.ValueStyles["err"] = lipgloss.NewStyle().Bold(true)
-log.Error("Whoops!", "err", "kitchen on fire")
+styles.Keys["err"] = lipgloss.NewStyle().Foreground(lipgloss.Color("204"))
+styles.Values["err"] = lipgloss.NewStyle().Bold(true)
+logger := log.New(os.Stderr)
+logger.SetStyles(styles)
+logger.Error("Whoops!", "err", "kitchen on fire")
 ```
 
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