Document all the possible cli command abbreviations

[chrisvelevitch]

Bug Report or Feature Request (mark with an x)

- [x] bug report -> please search issues before submitting
- [ ] feature request

Command (mark with an x)

- [ ] new
- [ ] build
- [ ] serve
- [ ] test
- [ ] e2e
- [ ] generate
- [ ] add
- [ ] update
- [ ] lint
- [ ] xi18n
- [ ] run
- [ ] config
- [ ] help
- [ ] version
- [x] doc

Desired functionality

I've seen examples of command abbreviations like ng g c <component-name> to generate components and ng g cl <class-name> to generate classes, but these are undocmented.

All the the possible abbreviations ought to be documented.

[adampenn]

Haven't contributed to a lot of projects before but I'd be happy to take this issue.

[adampenn]

I created a PR and signed the CLA let me know if there is anything else I need to do.

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