page-header: grammar improvement (display transfer rate)

Closes #10068

docs/cmdline-opts/page-header

@@ -161,9 +161,9 @@ curl can do TFTP downloads and uploads.
 .SH "PROGRESS METER"
 curl normally displays a progress meter during operations, indicating the
 amount of transferred data, transfer speeds and estimated time left, etc. The
-progress meter displays number of bytes and the speeds are in bytes per
-second. The suffixes (k, M, G, T, P) are 1024 based. For example 1k is 1024
-bytes. 1M is 1048576 bytes.
+progress meter displays the transfer rate in bytes per second. The suffixes
+(k, M, G, T, P) are 1024 based. For example 1k is 1024 bytes. 1M is 1048576
+bytes.
 
 curl displays this data to the terminal by default, so if you invoke curl to
 do an operation and it is about to write data to the terminal, it