docs: add sample code to readme

readme.md

@@ -1,4 +1,4 @@
-# eGo
+## eGo
 
 [![build](https://img.shields.io/github/actions/workflow/status/Tochemey/ego/build.yml?branch=main)](https://github.com/Tochemey/ego/actions/workflows/build.yml)
 [![codecov](https://codecov.io/gh/Tochemey/ego/branch/main/graph/badge.svg?token=Z5b9gM6Mnt)](https://codecov.io/gh/Tochemey/ego)
@@ -7,7 +7,7 @@
 eGo is a minimal library that help build event-sourcing and CQRS application through a simple interface, and it allows developers to describe their commands, events and states are defined using google protocol buffers.
 Under the hood, ego leverages [goakt](https://github.com/Tochemey/goakt) to scale out and guarantee performant, reliable persistence.
 
-## Features
+### Features
 
 - Write Model:
     - Commands handler: The command handlers define how to handle each incoming command,
@@ -26,13 +26,147 @@ Under the hood, ego leverages [goakt](https://github.com/Tochemey/goakt) to scal
     - [Cluster Mode](https://github.com/Tochemey/goakt#clustering)
 - Examples (check the [examples](./example))
 
-## Installation
+### Installation
 
 ```bash
 go get github.com/tochemey/ego
 ```
 
-## Contribution
+### Sample
+
+```go
+package main
+
+import (
+	"context"
+	"errors"
+	"log"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"github.com/google/uuid"
+	"github.com/tochemey/ego"
+	"github.com/tochemey/ego/eventstore/memory"
+	samplepb "github.com/tochemey/ego/example/pbs/sample/pb/v1"
+	"google.golang.org/protobuf/proto"
+)
+
+func main() {
+	// create the go context
+	ctx := context.Background()
+	// create the event store
+	eventStore := memory.NewEventsStore()
+	// create the ego engine
+	e := ego.NewEngine("Sample", eventStore)
+	// start ego engine
+	_ = e.Start(ctx)
+	// create a persistence id
+	entityID := uuid.NewString()
+	// create an entity behavior with a given id
+	behavior := NewAccountBehavior(entityID)
+	// create an entity
+	entity, _ := ego.NewEntity[*samplepb.Account](ctx, behavior, e)
+
+	// send some commands to the pid
+	var command proto.Message
+	// create an account
+	command = &samplepb.CreateAccount{
+		AccountId:      entityID,
+		AccountBalance: 500.00,
+	}
+	// send the command to the actor. Please don't ignore the error in production grid code
+	account, _, _ := entity.SendCommand(ctx, command)
+
+	log.Printf("current balance: %v", account.GetAccountBalance())
+
+	// send another command to credit the balance
+	command = &samplepb.CreditAccount{
+		AccountId: entityID,
+		Balance:   250,
+	}
+	account, _, _ = entity.SendCommand(ctx, command)
+	log.Printf("current balance: %v", account.GetAccountBalance())
+
+	// capture ctrl+c
+	interruptSignal := make(chan os.Signal, 1)
+	signal.Notify(interruptSignal, os.Interrupt, syscall.SIGINT, syscall.SIGTERM)
+	<-interruptSignal
+
+	// stop the actor system
+	_ = e.Stop(ctx)
+	os.Exit(0)
+}
+
+// AccountBehavior implements persistence.Behavior
+type AccountBehavior struct {
+	id string
+}
+
+// make sure that AccountBehavior is a true persistence behavior
+var _ ego.EntityBehavior[*samplepb.Account] = &AccountBehavior{}
+
+// NewAccountBehavior creates an instance of AccountBehavior
+func NewAccountBehavior(id string) *AccountBehavior {
+	return &AccountBehavior{id: id}
+}
+
+// ID returns the id
+func (a *AccountBehavior) ID() string {
+	return a.id
+}
+
+// InitialState returns the initial state
+func (a *AccountBehavior) InitialState() *samplepb.Account {
+	return new(samplepb.Account)
+}
+
+// HandleCommand handles every command that is sent to the persistent behavior
+func (a *AccountBehavior) HandleCommand(_ context.Context, command ego.Command, _ *samplepb.Account) (event ego.Event, err error) {
+	switch cmd := command.(type) {
+	case *samplepb.CreateAccount:
+		// TODO in production grid app validate the command using the prior state
+		return &samplepb.AccountCreated{
+			AccountId:      cmd.GetAccountId(),
+			AccountBalance: cmd.GetAccountBalance(),
+		}, nil
+
+	case *samplepb.CreditAccount:
+		// TODO in production grid app validate the command using the prior state
+		return &samplepb.AccountCredited{
+			AccountId:      cmd.GetAccountId(),
+			AccountBalance: cmd.GetBalance(),
+		}, nil
+
+	default:
+		return nil, errors.New("unhandled command")
+	}
+}
+
+// HandleEvent handles every event emitted
+func (a *AccountBehavior) HandleEvent(_ context.Context, event ego.Event, priorState *samplepb.Account) (state *samplepb.Account, err error) {
+	switch evt := event.(type) {
+	case *samplepb.AccountCreated:
+		return &samplepb.Account{
+			AccountId:      evt.GetAccountId(),
+			AccountBalance: evt.GetAccountBalance(),
+		}, nil
+
+	case *samplepb.AccountCredited:
+		bal := priorState.GetAccountBalance() + evt.GetAccountBalance()
+		return &samplepb.Account{
+			AccountId:      evt.GetAccountId(),
+			AccountBalance: bal,
+		}, nil
+
+	default:
+		return nil, errors.New("unhandled event")
+	}
+}
+```
+
+
+### Contribution
 
 Contributions are welcome!
 The project adheres to [Semantic Versioning](https://semver.org) and [Conventional Commits](https://www.conventionalcommits.org/en/v1.0.0/).
@@ -44,7 +178,7 @@ To contribute please:
 - Create a feature branch
 - Submit a [pull request](https://help.github.com/articles/using-pull-requests)
 
-### Test & Linter
+#### Test & Linter
 
 Prior to submitting a [pull request](https://help.github.com/articles/using-pull-requests), please run: