add local environment notes

terraform/README_LOCAL_ENV.md

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+# Malachite Terraform – local environment notes
+
+This document gives a short overview of how to approach the Terraform
+configuration in this directory when working on Malachite infrastructure.
+
+## 1. Layout
+
+Typical elements you may find here:
+
+- `modules/` – reusable building blocks used by multiple environments.
+- `envs/` or `workspaces/` – concrete environments (for example `dev`, `staging`, `prod`).
+- `variables.tf` / `terraform.tfvars` – input variables and their default values.
+
+Check the actual files in this directory to confirm the current layout.
+
+## 2. Safe local workflow
+
+When experimenting with Terraform changes:
+
+1. Select or create a dedicated development workspace.
+2. Run `terraform fmt` to keep files formatted.
+3. Use `terraform validate` to catch obvious issues before planning.
+4. Use `terraform plan` to review changes with your team before applying them.
+
+## 3. Contribution tips
+
+- Avoid committing real secrets; use variables and examples instead.
+- Add comments near non-obvious resources explaining why they are needed.
+- When adding new variables, update any example `tfvars` files to keep them in sync.