README: add the one-paragraph canonical description (hs-facts-v1); spell the name as Japan Construction Cost Database

Card: related datasets, JCCDB v5.0 observation layer (ogasurfproject/jccdb-observations) and USCCDB (ogasurfproject/usccdb)

v4.0: add README.md

the dataset now has its own DOI, distinct from the papers

stop shipping prices under the JCCDB name, and say so in the same commit

Overhaul dataset card: JCCDB v2.1 catalog, viewer configs, bilingual

Update README.md

Update README.md

Update README.md

Update README.md

README.md

Update README.md

initial commit