Create document explaining transaction rate

Transaction rate is ultimately limited by computational power and bandwidth, but there are two parameters that control the rate the network operates at:

* Block publication interval (currently 10 seconds)
* Block size (measured in bytes, currently 32kB)

These parameters are adjustable.

Transactions have variable byte size, so the block size measured in number of transactions is also variable.

If the total size of transactions in the unconfirmed pool exceeds the max block size at the time of block creation, the transactions are prioritized by the number of coin hours destroyed per byte.

Given the current parameters of 10 seconds and 32kB per block, the max transaction rate can be calculated by using the smallest possible transaction size (a transaction with one input and one output). The actual transaction rate will be less, since transactions will often have multiple inputs and two outputs (an additional output for change), increasing the average transaction size.