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: refs/heads/master@{#393979}
1 file changed