docs: Documentation bug fixes in README snippets

[stefanskid]

Description

The changes apply to the snippets in the README because they did not reflect the modules code after the refactor.

Motivation and Context

#81

How Has This Been Tested?

The snippets were tested manually. After the applied changes, all snippets no longer throw errors during terraform plan.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes if appropriate.
• All new and existing tests passed.

[acelebanski]

Great work in general! My comments are mostly referring to the same thing (placeholders). You can even add a TODO comment next to each placeholder, e.g.:

subnet_id = "/subscription/xxxx/......." # TODO: Put your existing subnet ID here

[acelebanski]

LGTM 👍