docs(fix): cleaned example command for running tests

[tikhoplav]

The command posted at the front page of the documentation
currently is not executable as is, it contains trailing spaces at the first line, which causes script to fail:

$ cargo run --profile ethtests -p revme -- \                                           
statetest \
../ethtests/GeneralStateTests/ \
../ethtests/LegacyTests/Constantinople/GeneralStateTests/ \
bins/revme/tests/EIPTests/StateTests/stEIP5656-MCOPY/ \
bins/revme/tests/EIPTests/StateTests/stEIP1153-transientStorage/
    Finished ethtests [optimized + debuginfo] target(s) in 0.13s
     Running `target/ethtests/revme ' '`
error: The subcommand ' ' wasn't recognized

USAGE:
	revme help <subcommands>...

For more information try --help
statetest: command not found

After this minor fix:

$ cargo run --profile ethtests -p revme -- \
    statetest \
    ../ethtests/GeneralStateTests/ \
    ../ethtests/LegacyTests/Constantinople/GeneralStateTests/ \
    bins/revme/tests/EIPTests/StateTests/stEIP5656-MCOPY/ \
    bins/revme/tests/EIPTests/StateTests/stEIP1153-transientStorage/
    Finished ethtests [optimized + debuginfo] target(s) in 0.12s
     Running `target/ethtests/revme statetest ../ethtests/GeneralStateTests/ ../ethtests/LegacyTests/Constantinople/GeneralStateTests/ bins/revme/tests/EIPTests/StateTests/stEIP5656-MCOPY/ bins/revme/tests/EIPTests/StateTests/stEIP1153-transientStorage/`

Running tests in ../ethtests/GeneralStateTests/...
██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████ 2621/2621Finished execution. Total CPU time: 22.385226s
All tests passed!

Running tests in ../ethtests/LegacyTests/Constantinople/GeneralStateTests/...
████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████ 0/0Finished execution. Total CPU time: 0.000000s
All tests passed!

Running tests in bins/revme/tests/EIPTests/StateTests/stEIP5656-MCOPY/...
████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████ 0/0Finished execution. Total CPU time: 0.000000s
All tests passed!

Running tests in bins/revme/tests/EIPTests/StateTests/stEIP1153-transientStorage/...
████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████ 0/0Finished execution. Total CPU time: 0.000000s
All tests passed!

[rakita]

Thank you!