etc/defaults.conf: add XBPS_UPDATE_CHECK_VERBOSE

closes #38076

Author: classabbyamp

etc/defaults.conf

@@ -158,3 +158,9 @@ XBPS_SUCMD="sudo /bin/sh -c"
 # When unset, newly build package overwrites the older one.
 #
 #XBPS_PRESERVE_PKGS=yes
+
+# [OPTIONAL]
+# Show more detailed output in ./xbps-src update-check. Useful for debugging.
+# This can also be set or exported as a regular environment variable.
+#
+#XBPS_UPDATE_CHECK_VERBOSE=yes