doc: limit-rate clarify base unit

[jsoref]

curl/docs/cmdline-opts/limit-rate.d

Lines 12 to 13 in 3085ccf

	Appending 'k' or 'K' will count the number as kilobytes, 'm' or 'M' makes it
	megabytes, while 'g' or 'G' makes it gigabytes. Examples: 200K, 3m and 1G.

I presume that this k is 2^10, but Wikipedia pretends it means 10^3. (I'm not endorsing this notation, but docs should be clear.)

[bagder]

They're all 1024-based. So K is 1024, M is 1024 * 1024 and G is 1024 * 1024 * 1024.

[jsoref]

I don't have prose and I'm not sure how many places should mention it, but this seems like a place that should include it. Happy to talk it out online.

[jsoref]

curl/docs/cmdline-opts/page-header

Line 164 in 265b14d

second. The suffixes (k, M, G, T, P) are 1024 based. For example 1k is 1024