Mention that it's only necessary to escape the '-' in chat scripts

twice (once for the arg parsing and once to make it a normal character).
Make the man page example consistent.

Reminded by: Bryan Liesner <bleez@netaxs.com>

usr.sbin/ppp/README.changes

@@ -98,3 +98,5 @@ o Ppp now waits either the full ``set cd'' time or until carrier is detected
 o The -alias flag has been deprecated.  The -nat flag should be used instead.
 o Unbalanced quotes in commands are now warned about and the entire command
   is ignored.
+o It is now only necessary to escape the `-' character in chat scripts twice.
+  See the example files for details.

usr.sbin/ppp/ppp.8

@@ -3886,7 +3886,7 @@ is running in interactive mode, file descriptor 3 is attached to
 For example (wrapped for readability);
 .Bd -literal -offset indent
 set login "TIMEOUT 5 \\"\\" \\"\\" login:--login: ppp \e
-word: ppp \\"!sh \\\\\\\\-c \\\\\\"echo \\\\\\\\-n label: >&2\\\\\\"\\" \e
+word: ppp \\"!sh \\\\-c \\\\\\"echo \\\\-n label: >&2\\\\\\"\\" \e
 \\"!/bin/echo in\\" HELLO"
 .Ed
 .Pp

usr.sbin/ppp/ppp.8.m4

@@ -3886,7 +3886,7 @@ is running in interactive mode, file descriptor 3 is attached to
 For example (wrapped for readability);
 .Bd -literal -offset indent
 set login "TIMEOUT 5 \\"\\" \\"\\" login:--login: ppp \e
-word: ppp \\"!sh \\\\\\\\-c \\\\\\"echo \\\\\\\\-n label: >&2\\\\\\"\\" \e
+word: ppp \\"!sh \\\\-c \\\\\\"echo \\\\-n label: >&2\\\\\\"\\" \e
 \\"!/bin/echo in\\" HELLO"
 .Ed
 .Pp