Improve log documentation

include/SDL3/SDL_log.h

@@ -56,6 +56,15 @@
  * - Windows: debug output stream
  * - Android: log output
  * - Others: standard error output (stderr)
+ *
+ * You don't need to have a newline (`\n`) on the end of messages, the
+ * functions will do that for you. For consistent behavior cross-platform, you
+ * shouldn't have any newlines in messages, such as to log multiple lines in
+ * one call; unusual platform-specific behavior can be observed in such usage.
+ * Do one log call per line instead, with no newlines in messages.
+ *
+ * Each log call is atomic, so you won't see log messages cut off one another
+ * when logging from multiple threads.
  */
 
 #ifndef SDL_log_h_