message: docs: add missing docs for snapshot
diff: @@ -4,7 +4,7 @@ version = "0.38.0-pre"
  license = "MIT"
  authors = ["Nervos Core Dev <dev@nervos.org>"]
  edition = "2018"
  -description = "TODO(doc): @zhangsoledad crate description"
  +description = "The ckb rocksdb snapshot wrapper"
  homepage = "https://github.com/nervosnetwork/ckb"
  repository = "https://github.com/nervosnetwork/ckb"
  