Updated doc to include client token file and engine run examples.
Updated doc to include client token file and engine run examples.

This change to running.md addresses points brought up by Shenghua@.
These include an example of a client token file which path is to be provided
on the command line, and the readdition of an example engine run.

Review-Url: https://codereview.chromium.org/1987483002
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#393979}

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