Method description should be more flexible

[bl-young]

e.g., information about mapping is not needed for inventory methods:

LCIAformatter/lciafmt/data/description.yaml

Lines 10 to 20 in b16f092

	[Method] flowable and context input files are maintained in the FEDEFL
	GitHub Repository: https://github.com/USEPA/fedelemflowlist
	The LCIA Formatter (https://github.com/USEPA/LCIAformatter) applies [Method]
	characterization factors to flows using the mapping housed in the FEDEFL.
	The flowable and context input files for [Method] are used by the LCIA Formatter
	to translate the names from the [Method] source file and generate a mapping
	file for the FEDEFL. This file contains all of the accepted flowable and context
	combinations which can be mapped to [Method] characterization factors. It also
	includes target UUID, units, and conversion factors as well as tracking
	who mapped and verified each record and when they were last updated.