Improve doc comment for GIDSignInButtonStyle (#204)

Co-authored-by: w-goog <[email protected]>

Author: kamimi01

GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignInButton.h

@@ -25,9 +25,9 @@ NS_ASSUME_NONNULL_BEGIN
 ///
 /// The minimum size of the button depends on the language used for text.
 /// The following dimensions (in points) fit for all languages:
-/// - kGIDSignInButtonStyleStandard: 230 x 48
-/// - kGIDSignInButtonStyleWide:     312 x 48
-/// - kGIDSignInButtonStyleIconOnly: 48 x 48 (no text, fixed size)
+/// - kGIDSignInButtonStyleStandard: 230 x 48 (Example display text: "Sign in")
+/// - kGIDSignInButtonStyleWide:     312 x 48 (Example display text: "Sign in with Google")
+/// - kGIDSignInButtonStyleIconOnly: 48 x 48  (no text, fixed size)
 typedef NS_ENUM(NSInteger, GIDSignInButtonStyle) {
   kGIDSignInButtonStyleStandard = 0,
   kGIDSignInButtonStyleWide = 1,