Improve documentation around deprecations

glib/docs.c

@@ -2051,6 +2051,14 @@
  * Since: 2.32
  */
 
+/**
+ * GLIB_DISABLE_DEPRECATION_WARNINGS:
+ *
+ * A macro that should be defined before including the glib.h header.
+ * If it is defined, no compiler warnings will be produced for uses
+ * of deprecated GLib APIs.
+ */
+
 /**
  * G_GNUC_NORETURN:
  *