dev-docs: document provider usage

Signed-off-by: Moritz Sanft <[email protected]>

dev-docs/workflows/terraform-provider.md

@@ -0,0 +1,32 @@
+# Constellation Terraform Provider
+
+This document explains the basic ways of working with the [Constellation Terraform Provider](../../terraform-provider-constellation/).
+
+## Building the Terraform Provider
+
+The Constellation Terraform provider can be built through Bazel, either via the [`devbuild` target](./build-develop-deploy.md) (recommended), which will create a `terraform` directory
+with the provider binary and some utility files in the current working directory, or explicitly via this command:
+
+```bash
+bazel build //terraform-provider-constellation:tf_provider
+```
+
+## Using the Terraform Provider
+
+The Terraform provider binary can be used with the normal Terraform CLI, by setting a [development override](https://developer.hashicorp.com/terraform/cli/config/config-file#development-overrides-for-provider-developers),
+so that the registry path to the provider is replaced with the path to the locally built provider. If using the [`devbuild` target](./build-develop-deploy.md), a `config.tfrc` file with the override set to the path
+of the built binary is placed automatically in the `terraform` directory in the current working directory. Otherwise, the file can be also built and copied to the current working directory explicitly via this command:
+
+```bash
+bazel build //terraform-provider-constellation:terraform_rc
+cp bazel-bin/terraform-provider-constellation/config.tfrc .
+sed -i "s|@@TERRAFORM_PROVIDER_PATH@@|$(realpath bazel-bin/terraform-provider-constellation/tf_provider_/tf_provider)|g" config.tfrc
+```
+
+Afterwards, all Terraform commands that should use the local provider build should be prefixed with `TF_CLI_CONFIG_FILE=config.tfrc` like so:
+
+```bash
+TF_CLI_CONFIG_FILE=config.tfrc terraform init
+TF_CLI_CONFIG_FILE=config.tfrc terraform apply
+...
+```