doc: update document.

Author: jaywcjlove

README.md

@@ -65,6 +65,7 @@ Set editor placeholder string:
 
 ```swift
 TextEditorPlus(text: $text)
+    //.font(NSFont(name: "pencontrol", size: 12)!)
     .font(.systemFont(ofSize: CGFloat(Float(fontSize)!), weight: .regular))
     .textSetting("Test placeholder string", for: .placeholderString)
 ```

Sources/TextEditorPlus/Settings/Font.swift

@@ -35,6 +35,7 @@ extension TextEditorPlus {
     /// 
     /// ```swift
     /// TextEditorPlus(text: $text)
+    ///    .font(NSFont(name: "pencontrol", size: 12)!)
     ///    .font(.systemFont(ofSize: 24, weight: .regular))
     /// ```
     public func font(_ value: FontHelper) -> Self {