doc: add README.md for terraform modules

[mglotov]

Prerequisites

Please answer the following questions for yourself before submitting an issue. YOU MAY DELETE THE PREREQUISITES SECTION.

• I am running the latest version
• I checked the documentation and found no answer
• I checked to make sure that this issue has not already been filed

Expected Behavior

All modules have README.md

Current Behavior

Terraform modules don't have README.md, even generated via terraform-docs