Tf 0.12 readme details + Makefile w/ git-release

[exequielrafaela]

Updating terraform-aws-cost-billing-alarm repo:

📓 Summary

1. Updating README.md with tf 0.12 release info

Releases
Versions: <= 0.x.y (Terraform 0.11.x compatible)

eg: https://registry.terraform.io/modules/binbashar/cost-budget/aws/0.0.1
Versions: >= 1.x.y (Terraform 0.12.x compatible -> WIP)

eg: https://registry.terraform.io/modules/binbashar/cost-budget/aws/1.0.0

2. Adding Makefile to follow the new standard dockerized git-release cross-project modules approach release tagging.
   Since the need of generating consistent cross-project versioning tagging we've decided to automate this task in our Makefiles.
   Ref: Bbl 33 billing review public-docker-images#10

👨‍💻 New Commits

• adding tf 0.12 related readme.md updates
• updating tf 0.12 related readme.md with exact release ver
• Adding git-release support in makefile with git-chglog and semtag

🚩 Post Tasks

• Update release tag 0.0.2 after PR merged to master in order to reflect the updates at the Terraform Registry -> https://registry.terraform.io/modules/binbashar/cost-billing-alarm/aws/0.0.1.

🥇 TODO

• Add terratest to this module.
• Add new version 1.0.0 with tf-0.12 support.