[Doc] Reth snapshots not work

[TangMonk]

untar the base-mainnet-reth-1737128189.tar.zst snapshots to ./reth-data/

Structure is:

 reth-data/
     snapshots/
         mainnet/
            download/

files inside download folder:

$ ls snapshots/mainnet/download/

blobstore  db  invalid_block_hooks  known-peers.json  reth.toml  snapshots  static_files

Then I CLIENT=reth docker compose up, It still sync from 0 block