Add development instructions

Signed-off-by: Danny Kopping <[email protected]>

Author: dannykopping

README.md

@@ -1,3 +1,38 @@
 # terraform-provider-coder
 
-See [Coder](https://github.com/coder/coder).
+Terraform provider for [Coder](https://github.com/coder/coder).
+
+### Developing
+
+Follow the instructions outlined in the [Terraform documentation](https://developer.hashicorp.com/terraform/cli/config/config-file#development-overrides-for-provider-developers)
+to setup your local Terraform to use your local version rather than the registry version.
+
+1. Create a file named `.terraformrc` in your `$HOME` directory
+2. Add the following content:
+   ```hcl
+    provider_installation {
+        # Override the coder/coder provider to use your local version
+        dev_overrides {
+          "coder/coder" = "/path/to/terraform-provider-coder"
+        }
+
+        # For all other providers, install them directly from their origin provider
+        # registries as normal. If you omit this, Terraform will _only_ use
+        # the dev_overrides block, and so no other providers will be available.
+        direct {}
+    }
+   ```
+3. (optional, but recommended) Validate your configuration:
+    1. Create a new `main.tf` file and include:
+      ```hcl
+      terraform {
+          required_providers {
+              coder = {
+                  source = "coder/coder"
+              }
+          }
+      }
+      ```
+   2. Run `terraform init` and observe a warning like `Warning: Provider development overrides are in effect`
+4. Run `go build -o terraform-provider-coder` to build the provider binary, which Terraform will try locate and execute
+5. All local Terraform runs will now use your local provider!