fix usage documentation

[brodycj]

Platforms affected

all

Motivation and Context

see #206: some of the usage commands do not look right, and I did encounter some issues when copy-pasting into my shell

(the updates from both this PR and PR #208 are needed to resolve the issue)

Description

• update documentation & usage commands
• show the commands with node prefix, with note that the node prefix is only needed on Windows

Testing

• copy-pasted the updated commands into my shell
• run the mobile spec app on at least one platform such as Android
• test the updated usage on Windows

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary