Improve docs for toml based tasks

[jatinn]

one of the examples on the page https://mise.jdx.dev/tasks/toml-tasks.html#toml-based-tasks is

[tasks.test]
description = 'Run automated tests'
run = [ # multiple commands are run in series
    'cargo test',
    './scripts/test-e2e.sh',
]
dir = "{{cwd}}" # run in user's cwd, default is the project's base directory

however the comment about the dir option seems incorrect based on my testing, for toml tasks using the dir option almost always caused the task to fail. also the default seems to be the cwd instead of the project root, would be good to get some clarity around the correct behaviour.

feel like the confusion from the docs is what led to folks opening:

• jdx/mise#1722
• jdx/mise#1713