Building book doesn't work

[jmole]

I'm following the instructions here: https://github.com/paritytech/polkadot/tree/master/roadmap/implementers-guide

   Installed package `mdbook v0.4.14` (executable `mdbook`)
   Installed package `mdbook-linkcheck v0.7.6` (executable `mdbook-linkcheck`)
   Installed package `mdbook-graphviz v0.1.3` (executable `mdbook-graphviz`)

~/code/polkadot master ❯ mdbook serve roadmap/implementers-guide
2021-12-18 19:22:18 [INFO] (mdbook::book): Book building has started
No such file or directory (os error 2)
2021-12-18 19:22:18 [ERROR] (mdbook::utils): Error: The "graphviz" preprocessor exited unsuccessfully with exit status: 1 status

[ordian]

You might need to install graphviz itself (e.g. sudo apt-get install graphviz on Ubuntu).

[jmole]

that's it thanks. Submitted pull request here: #4565