top: update user/system cpu % graph content (man page)

What had been stated as the contents of the cpu graphs
was never really inclusive enough. Those recent newlib
tweaks highlighted the need for these man doc changes.

Signed-off-by: Jim Warner <james.warner@comcast.net>

top/top.1

@@ -62,7 +62,7 @@
 .
 .\" Document /////////////////////////////////////////////////////////////
 .\" ----------------------------------------------------------------------
-.TH TOP 1 "July 2020" "procps-ng" "User Commands"
+.TH TOP 1 "September 2020" "procps-ng" "User Commands"
 .\" ----------------------------------------------------------------------
 .nh
 
@@ -521,8 +521,9 @@ an abbreviated summary is shown consisting of these elements:
 
 .fi
 
-Where: a) is the combined \fBus\fR and \fBni\fR percentage; b) is the \fBsy\fR percentage; c) is the total;
-and d) is one of two visual graphs of those representations.
+Where: a) is the `user' (us + ni) percentage; b) is the `system'
+(sy + hi + si) percentage; c) is the total; and d) is one of two
+visual graphs of those representations.
 \*(XT 4b. SUMMARY AREA Commands and the `t' command for additional information
 on that special 4-way toggle.