Improve usage documentation

[SharkFourSix]

The example on the repo page only depicts usage of a single rule.

1. How do you use multiple rules on a single field?
2. Do we have to manually add the included rules all the time when we instantiate the validator?

[guiferpa]

Hey @SharkFourSix , sorry for delay.

🌵 Currently this project really doesn't have a detailed documentation, let's join effort for it, be my guest to help the project.

1. How do you use multiple rules on a single field?
   There's a folder named examples with some examples about implementations. For specifically multiple rules I hope this example help you

2. Do we have to manually add the included rules all the time when we instantiate the validator?
   Unfortunately yes, gody was built thinking about many packages for different configurations then in this way you can have many packages with different instances with your each config validator.

package foo

import (
	"github.com/guiferpa/gody/v2"
	"github.com/guiferpa/gody/v2/rule"
)

var (
	Validator    *gody.Validator
	DefaultRules []gody.Rule
)

func init() {
	DefaultRules = []gody.Rule{rule.NotEmpty}
	Validator = gody.NewValidator()
	Validator.AddRules(DefaultRules...)
}

package bar

import (
	"github.com/guiferpa/gody-sample/foo"

	"github.com/guiferpa/gody/v2"
	"github.com/guiferpa/gody/v2/rule"
)

var (
	Validator    *gody.Validator
	DefaultRules []gody.Rule
)

func init() {
	DefaultRules = []gody.Rule{rule.Min}
	Validator = gody.NewValidator()
	Validator.AddRules((append(DefaultRules, foo.DefaultRules...))...)
}

package main

import (
	"fmt"

	"github.com/guiferpa/gody-sample/bar"
	"github.com/guiferpa/gody-sample/foo"
)

type FooBar struct {
	Attribute string `validate:"not_empty"`
}

func main() {
	foobar := FooBar{}
	if _, err := foo.Validator.Validate(foobar); err != nil {
		fmt.Println(err) // field attribute cannot be empty
	}
	if _, err := bar.Validator.Validate(foobar); err != nil {
		fmt.Println(err) // field attribute cannot be empty
	}
}