Add "Version 1.1.0 ends here" comments

include/avif/avif.h

diff --git a/include/avif/avif.h b/include/avif/avif.h
index 41daaec..df7c0dc 100644
--- a/include/avif/avif.h
+++ b/include/avif/avif.h
@@ -1294,6 +1294,8 @@
     // to the appropriate source.
     avifBool imageSequenceTrackPresent;
 
+    // Version 1.1.0 ends here. Add any new members after this line.
+
 #if defined(AVIF_ENABLE_EXPERIMENTAL_GAIN_MAP)
     // This is true when avifDecoderParse() detects a gain map.
     avifBool gainMapPresent;
@@ -1495,6 +1497,8 @@
     // Defaults to AVIF_HEADER_FULL
     avifHeaderFormat headerFormat;
 
+    // Version 1.1.0 ends here. Add any new members after this line.
+
 #if defined(AVIF_ENABLE_EXPERIMENTAL_GAIN_MAP)
     int qualityGainMap; // changeable encoder setting
 #endif