Edit and expand command docs

[jbogarthyde]

This one is just the top-level commands. Will do separate PR for subcommands (generation schematics).

[hansl]

Overall looks good. 3 comments by Alan and I.

[jbogarthyde]

Please provide an example using the run command with the universal target. I would like to add it to the long description:
"Additional predefined Architect targets are available that do not correspond to CLI commands. For example, ..."

[alan-agius4]

@jbogarthyde that would be

ng run <project>:server

// prod
ng run <project>:server:production 

[jbogarthyde]

@hansl I have addressed your requested changes - please check and remove blocker.
@alan-agius4
Do either of you know why it's failing continuous-integration?

[alan-agius4]

Thanks so much, Left one small comment.

[jbogarthyde]

Moved these commits to docs-preview branch - PR Docs preview #12837

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