…dataset to be BIDS dataset

This is my take on an extended discussion about ambiguity of
`rawdata/` example:
https://github.com/bids-standard/bids-specification/pull/1734/files#r1534475631

Prior one bundled naming aspect under the same MUST. I separated into
separate sentences, added explicit statement that BIDS does not
prescribe a particular naming scheme for source data. And added
explicit RECOMMENDED on the example how to organize/name files there.

…y a BIDS dataset

…mpliant'

=== Do not change lines below ===
{
 "chain": [],
 "cmd": "sed -i -e s,rawdata,noncompliant,g tools/schemacode/bidsschematools/validator.py tools/schemacode/bidsschematools/tests/test_validator.py tools/schemacode/bidsschematools/tests/data/expected_bids_validator_xs_write.log",
 "exit": 0,
 "extra_inputs": [],
 "inputs": [],
 "outputs": [],
 "pwd": "."
}
^^^ Do not change lines above ^^^

…aset

…underscores too

Co-authored-by: Chris Markiewicz <effigies@gmail.com>