HACKING.md of indigo needs to be updated.

[itaru2622]

when I run operations described in indigo/HACKING.md, It's failed as below:

go run ./cmd/lexgen/ --package bsky --prefix app.bsky --outdir api/bsky ../atproto/lexicons/app/bsky
:
panic: missing ref: "com.atproto.label.defs#label"
:
exit status 2

# below command didn't get error  but not sure it is correct operation.
go run ./cmd/lexgen/ --package bsky --prefix app.bsky --outdir api/bsky ../atproto/lexicons

currently, indigo has api/ozone and api/chat folders but no descriptions how to re-generate those.
not sure if there are any other updates needed.