docs: add CONTRIBUTING.md

Signed-off-by: Calum Murray <cmurray@redhat.com>

Author: Cali0707

CONTRIBUTING.md

@@ -0,0 +1,79 @@
+# Contributing
+
+Want to contribute to the Kubernetes extension? We recommend opening an issue first to discuss your proposed changes. Once aligned, refer to the guide below for development workflow.
+
+## Project Structure
+
+```
+cmd/main.go              # Entry point
+pkg/extension/
+  extension.go           # Extension struct, New(), Run()
+  client.go              # ResourceClient interface and adapter
+  resource.go            # Resource reference parsing helpers
+  operations.go          # Operation registration
+  create.go              # Create handler
+  wait.go                # Wait handler
+  delete.go              # Delete handler
+  *_test.go              # Unit tests
+```
+
+## Adding a New Operation
+
+1. Create `pkg/extension/<operation>.go` with your handler:
+
+```go
+func (e *Extension) handleMyOp(ctx context.Context, req *sdk.OperationRequest) (*sdk.OperationResult, error) {
+    if e.client == nil {
+        return sdk.Failure(fmt.Errorf("kubernetes client not initialized")), nil
+    }
+
+    args, ok := req.Args.(map[string]any)
+    if !ok {
+        return sdk.Failure(fmt.Errorf("args must be an object")), nil
+    }
+
+    // Your logic here
+
+    e.LogInfo(ctx, "Operation completed", map[string]any{"key": "value"})
+    return sdk.Success("Done"), nil
+}
+```
+
+2. Register the operation in `operations.go`:
+
+```go
+e.AddOperation(
+    sdk.NewOperation("myop",
+        sdk.WithDescription("Description of your operation"),
+        sdk.WithParams(jsonschema.Schema{
+            Type: "object",
+            Properties: map[string]*jsonschema.Schema{
+                "field": {Type: "string", Description: "Field description"},
+            },
+            Required: []string{"field"},
+        }),
+    ),
+    e.handleMyOp,
+)
+```
+
+3. Add tests in `pkg/extension/<operation>_test.go` using table-driven tests.
+
+## Testing
+
+Run all tests:
+```bash
+go test ./...
+```
+
+Run with verbose output:
+```bash
+go test ./... -v
+```
+
+## Code Style
+
+- Use `e.LogInfo()` and `e.LogError()` for logging
+- Return `sdk.Failure(err)` for errors, not Go errors
+- Use `parseResourceRef()` for standard resource arguments
+- Keep handlers focused on a single responsibility