Improve cargo example

[Fishrock123]

Adds restore-keys for cargo - this helps improve build times by allowing the cache to be mostly pre-populated when deps are updated.

Adds two missing cache files.

Adds a build type parameter to the cache keys to account for different build profiles / targets.

Description

Example improvement for use with cargo.

Motivation and Context

• Not all desired cache files were included
• Restoring the cache when deps change is very beneficial
• Easy build target parameter is very useful when using the cache for different build targets (very common to build debug for a tests job and release for some kind of publish job).

How Has This Been Tested?

It's docs

Screenshots (if appropriate):

Types of changes

• [x] Documentation (add or update README or docs)

Checklist:

• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.