Exclude transparent-clipping-excluded windows from updating the ignored region

Transparent clipping interacts poorly with programs whose transparent
interface elements must show windows below them for functionality,
for example screenshot utilities.

picom.sample.conf

@@ -355,6 +355,12 @@ use-damage = true;
 #
 # transparent-clipping = false
 
+# Specify a list of conditions of windows that should never have transparent
+# clipping applied. Useful for screenshot tools, where you need to be able to
+# see through transparent parts of the window.
+#
+# transparent-clipping-exclude = []
+
 # Set the log level. Possible values are:
 #  "trace", "debug", "info", "warn", "error"
 # in increasing level of importance. Case doesn't matter.