SDL_mixer: include: Adjust documentation to note that Mix_Init isn't required.

SDL Commits
1 
From d7741010a117ba7076e4b244403d6e885d9ef11c Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Tue, 18 Oct 2022 22:58:36 -0400
Subject: [PATCH] include: Adjust documentation to note that Mix_Init isn't
 required.

Fixes #464.
---
 include/SDL_mixer.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/SDL_mixer.h b/include/SDL_mixer.h
index 01d65add..b7272e6c 100644
--- a/include/SDL_mixer.h
+++ b/include/SDL_mixer.h
@@ -119,8 +119,12 @@ typedef enum
  * Initialize SDL_mixer.
  *
  * This function loads dynamic libraries that SDL_mixer needs, and prepares
- * them for use. This must be the first function you call in SDL_mixer, and if
- * it fails you should not continue with the library.
+ * them for use.
+ *
+ * Note that, unlike other SDL libraries, this call is optional! If you load
+ * a music file, SDL_mixer will handle initialization on the fly. This
+ * function will let you know, up front, whether a specific format will be
+ * available for use.
  *
  * Flags should be one or more flags from MIX_InitFlags OR'd together. It
  * returns the flags successfully initialized, or 0 on failure.