set placeholder fee for fee-calculating transaction

[rphair]

@katomm has already suggested a PR be opened for this.

This is a response to a documentation problem reported here, saying that the fee itself must be known before the transaction that calculates the fee. I believe this results from people running through the token creation exercises without yet having the basic transaction building experience (e.g. the process described here for stake pool operators).

The forum comment implies setting fee="0" occurs so early in the flow of the affected page-- where it's included with general variables for the testing environment-- that it's easily missed. I've moved it forward into the "Build the raw transaction" section so that the fee is initialised to zero immediately before that test transaction, along with an explanation of why the fee has to be specified twice (first an ignored value, then the calculated value).

[rphair]

I swear Github has promised in more than one place that it factors out "dos" vs. "unix" line terminations so they're not supposed to make a difference in the diffs. Will try to submit again with fileformat closer to the original (which was effectively "dos"). 😓

[katomm]

Great contribution, also thanks to @AndrewWestberg

[den-is]

Hey guys, so is that related to assets minting transactions fees or is useful for any ADA transaction too, as a good new "best practice"? (for example p2p ADA transactions, rewards withdrawal)