doc/md: add tutorial for configuring gRPC service method generation

doc/md/tutorial-grpc-service-generation-options.md

@@ -0,0 +1,51 @@
+---
+id: grpc-service-generation-options
+title: Configuring Service Method Generation
+sidebar_label: Service Generation Options
+---
+By default, entproto will generate CRUD service methods for an `ent.Schema` annotated with `ent.Service()`. Method generation can be customized by including the argument `entproto.Methods()` in the `entproto.Service()` annotation. `entproto.Methods()` accepts bit flags to determine what service methods should be generated. The flags include:
+```go
+// Generates a Create gRPC service method for the entproto.Service.
+entproto.MethodCreate
+
+// Generates a Get gRPC service method for the entproto.Service.
+entproto.MethodGet
+
+// Generates an Update gRPC service method for the entproto.Service.
+entproto.MethodUpdate
+
+// Generates a Delete gRPC service method for the entproto.Service.
+entproto.MethodDelete
+
+// Generates all service methods for the entproto.Service.
+// This is the same behavior as not including entproto.Methods.
+entproto.MethodAll
+```
+To generate a service with multiple methods, bitwise OR the flags.
+
+
+To see this in action, we can modify our ent schema. Let's say we wanted to prevent our gRPC client from mutating entries. We can accomplish this by modifying `ent/schema/user.go`:
+```go {5-8}
+func (User) Annotations() []schema.Annotation {
+	return []schema.Annotation{
+		entproto.Message(),
+		entproto.Service(
+			entproto.Methods(
+				entproto.MethodCreate |
+                entproto.MethodGet
+            ),
+        ),
+	}
+}
+```
+
+Re-running `go generate ./...` will give us the following service definition in `entpb.proto`:
+```protobuf
+service UserService {
+  rpc Create ( CreateUserRequest ) returns ( User );
+
+  rpc Get ( GetUserRequest ) returns ( User );
+}
+```
+
+Notice that the service no longer includes `Update` and `Delete` methods. Perfect!