curl.1: clarify --limit-rate's effect on both directions

Bug: http://curl.haxx.se/bug/view.cgi?id=1414
Reported-by: teo8976

docs/curl.1

@@ -877,9 +877,10 @@ of what your command-line operation does!
 If this option is used several times, the last given file name will be
 used. (Added in 7.16.1)
 .IP "--limit-rate <speed>"
-Specify the maximum transfer rate you want curl to use. This feature is useful
-if you have a limited pipe and you'd like your transfer not to use your entire
-bandwidth.
+Specify the maximum transfer rate you want curl to use - for both downloads
+and uploads. This feature is useful if you have a limited pipe and you'd like
+your transfer not to use your entire bandwidth. To make it slower than it
+otherwise would be.
 
 The given speed is measured in bytes/second, unless a suffix is appended.
 Appending 'k' or 'K' will count the number as kilobytes, 'm' or M' makes it