docs: Document custom templates variables

[mauriciabad]

In the readme/documentation add the variables avilable inside the .tmpl file.

go-enum/generator/generator.go

Lines 209 to 235 in 9d73c76

	data := map[string]any{
	"enum": enum,
	"name": name,
	"lowercase": g.LowercaseLookup,
	"nocase": g.CaseInsensitive,
	"nocomments": g.NoComments,
	"noIota": g.NoIota,
	"marshal": g.Marshal,
	"sql": g.SQL,
	"sqlint": g.SQLInt,
	"flag": g.Flag,
	"names": g.Names,
	"ptr": g.Ptr,
	"values": g.Values,
	"anySQLEnabled": g.anySQLEnabled(),
	"sqlnullint": g.SQLNullInt,
	"sqlnullstr": g.SQLNullStr,
	"mustparse": g.MustParse,
	"forcelower": g.ForceLower,
	"forceupper": g.ForceUpper,
	"noparse": g.NoParse,
	// Computed values for cleaner templates
	"generateParse": generateParse,
	"parseIsPublic": parseIsPublic,
	"parseName": parseName,
	"generateError": generateError,
	}

go-enum/generator/generator.go

Lines 42 to 48 in 9d73c76

	type Enum struct {
	Name string
	Prefix string
	Type string
	Values []EnumValue
	Comment string
	}

Would also be nice to include a small example that uses variables, if/else, importing an external library... In my case, I had to do this, maybe it's a good real-world example:

/enums/templates/huma.tmpl

// Schema returns the Huma schema for {{.enum.Name}}.
func (s {{.enum.Name}}) Schema(_ huma.Registry) *huma.Schema {
	values := {{.enum.Name}}Values()
	enumInterfaces := make([]any, len(values))
	for i, v := range values {
		enumInterfaces[i] = string(v)
	}

	return &huma.Schema{
		Type:        huma.TypeString,
		Enum:        enumInterfaces,{{- if .enum.Comment }}
		Description: {{ printf "%q" .enum.Comment }},{{- end }}
		Examples:    []any{string(values[0])},
	}
}

/enums/my_status.go

package enums

//go:generate go tool go-enum --marshal --template templates/*.tmpl --values

// MyStatus represents the status of the fetch request
// ENUM(pending, completed, failed)
type MyStatus string