Update images.md to follow style guide recommendations

Update page /docs/concepts/containers/images.md to follow
recommendations on the style guide of Kubernetes documentation:
* Make punctuation consistent across list items.
* Use upper camel case for API types.
* Remove unnecessary phrases.
* Include links to content within the same page.
* Fix small grammar and typos.
* Add missing periods in sentences.
* Use angle brackets in placeholders.

Author: stormqueen1990