README+docs: create document explaining decimal display and RFQ, add reference implementation #3136

Job	Run time
Format check	27s
cross compilation	4m 29s
Docker build check	3m 17s
Compilation check	47s
run itests	7m 52s
run itests postgres	20m 21s
Lint check	5m 55s
migration version check	19s
go mod check	2m 51s
RPC check	1m 16s
run LiT tests	8m 48s
sample configuration check	45s
Sqlc check	35s
test vector check	52s
run unit tests (unit-race)	7m 32s
run unit tests (unit-cover)	2m 32s
run unit tests (unit dbbackend=postgres)	5m 0s
finish	5s
	1h 13m 43s

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