curl.1: minor language fix

Bug: http://curl.haxx.se/mail/archive-2014-07/0006.html

docs/curl.1

@@ -103,8 +103,8 @@ any response data to the terminal.
 If you prefer a progress "bar" instead of the regular meter, \fI-#\fP is your
 friend.
 .SH OPTIONS
-Options start with one or two dashes. Many of the options require an addition
-value next to it.
+Options start with one or two dashes. Many of the options require an
+additional value next to them.
 
 The short "single-dash" form of the options, -d for example, may be used with
 or without a space between it and its value, although a space is a recommended