Improve Usage doc for `npm version`

[sympmarc]

General Information

• [ ] Usage
• [ ] Development
• [x] Documentation
• [ ] Feature Request

What Version you are running?

• @pnp/spfx: 1.9.0

Describe your problem

Being able to bump the version with this generator is a nice little helper. To me, the part of the Usage doc which explains it isn't very clear. The capability is built into the generator now, and it would be nice to have better docs about how to do it.

[sympmarc]

Is this section of the doc valid?

"The current commit will also be tagged on the git repository." plus the image.