(chore) fix reth book dockercmd with correct datadir path for volume

[0xprames]

correcting the volume mount in the book docker instructions

2023-09-23T23:00:19.201591Z  INFO reth::cli: Opening database path="/root/.local/share/reth/mainnet/db"
2023-09-23T23:00:19.222419Z  INFO reth::cli: Database opened

[codecov]

Codecov Report

Merging #4753 (c7c6ef8) into main (b7a6eed) will increase coverage by 0.00%.
The diff coverage is n/a.

see 8 files with indirect coverage changes

Flag	Coverage Δ
integration-tests	16.51% <ø> (+<0.01%)	⬆️
unit-tests	63.48% <ø> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
reth binary	32.11% <ø> (ø)
blockchain tree	83.73% <ø> (ø)
pipeline	88.53% <ø> (+0.01%)	⬆️
storage (db)	73.70% <ø> (ø)
trie	94.73% <ø> (ø)
txpool	49.50% <ø> (ø)
networking	77.12% <ø> (+0.02%)	⬆️
rpc	57.55% <ø> (ø)
consensus	63.09% <ø> (ø)
revm	28.33% <ø> (ø)
payload builder	8.32% <ø> (ø)
primitives	86.53% <ø> (+0.02%)	⬆️