patch 8.0.1089: cannot get range count in user command

Problem:    Cannot get range count in user command.
Solution:   Add <range> argument.
diff --git a/runtime/doc/map.txt b/runtime/doc/map.txt
index 983fb2d..f6bcde2 100644
--- a/runtime/doc/map.txt
+++ b/runtime/doc/map.txt
@@ -1415,6 +1415,8 @@
 	<line1>	The starting line of the command range.
 						*<line2>*
 	<line2>	The final line of the command range.
+						*<range>*
+	<range> The number of items in the command range: 0, 1 or 2
 						*<count>*
 	<count>	Any count supplied (as described for the '-range'
 		and '-count' attributes).