[fix] benchmark run with compose

[rdettai]

Which issue does this PR close?

Closes #665.

Rationale for this change

The the following command from the README:

docker-compose run ballista-client cargo run benchmark ballista --host ballista-scheduler --port 50050 --query 1 --path /data --format tbl

was failing because --host was taken as an option for docker-compose instead of cargo run benchmark.

Also binding to a folder outside the project folder:

  volumes:
    - ../..:/ballista

is dangerous as you might end up overriding random files on the host filesystem.

What changes are included in this PR?

Removed the binding to ../.. and documentation update.

Are there any user-facing changes?

No

[alamb]

Thanks @rdettai !

[Dandandan]

Looks good!