Rollup merge of #136396 - aDotInTheVoid:crate-isnt-package-whyyy, r=GuillaumeGomez

rustdoc-json-types: Document that crate name isn't package name.

This wasn't clear from the docs before: https://rust-lang.zulipchat.com/#narrow/channel/266220-t-rustdoc/topic/.E2.9C.94.20Getting.20external.20crate.20names.20as.20defined. CC `@kpreid`

r? `@GuillaumeGomez`

Author: fmease