ReadMe for "alloc" in “Operating a private network” should tell user to create accounts first

[FlashSheridan]

https://github.com/ethereum/go-ethereum#operating-a-private-network states “First, you'll need to create the genesis state of your networks… If you'd like to pre-fund some accounts for easier testing, you can populate the alloc field with account configs”. (Emphasis added.) As noted in a blog post (https://gettoshare.com/2017/10/30/how-to-use-genesis-json-alloc-property/) and responses to a previous bug report (#14831), the first-time reader of this ReadMe should normally create the accounts referenced in the alloc fields first. (The natural expectation of the intended audience for this ReadMe is probably something like the behavior of the --dev and --unlock options, but those are not documented here.)

I’ve already submitted two PRs to correct this; the first was rejected (#20001) and the revision (#20005) is in limbo. I’m filing a bug so that users can search the database for unfixed bugs containing "alloc", rather than having to search for blog posts.

[karalabe]

Fixed.