Add contribute documentation to project

[salami738]

Hi, i would like to suggest a contribution readme file in the project root.

Example:

# How to contribute

- Fork original repository on github: https://github.com/dodevops
- Clone forked repo here: https://github.com/salami738/terraform-azure-kubernetes/tree/main
- Alternatively: Sync already forked repo to original
	git remote add upstream git@github.com:dodevops/terraform-azure-kubernetes.git
	~/workspace/dodevops/terraform-azure-kubernetes$ git fetch upstream
	git checkout main
	git rebase upstream/main
	git push origin main

- Make changes
- Reformat
- Generate documentation: docker run -v "$PWD":/terraform ghcr.io/dodevops/terraform-module-tools:latest
- ATTENTION: Rebase vs ...
- Git commit
	- Use [conventional commits](https://www.conventionalcommits.org/en/v1.0.0/)
	- Example: "feat: Feature 1"
	- Example: "fix: Bugfix for feature 1"
- Git squash, if needed
- Push to fork
- Create PR to original repo

- Wait for devops to review
- Wait for devops to push to terraform registry

- Update project terraform sources: https://registry.terraform.io/modules/dodevops/kubernetes/azure/latest

[salami738]

https://pre-commit.com/ could be an interesting addition.