Add readme (#2)

README.md

@@ -0,0 +1,37 @@
+# go-ecs
+
+go-ecs is a library for querying [ECS][ecs] fields by name to obtain the fields
+definition (e.g. Elasticsearch field data type, description, etc).
+
+The library includes data from tagged released of [elastic/ecs][ecs_repo].
+
+[ecs]: https://www.elastic.co/guide/en/ecs/current/index.html
+[ecs_repo]: https://github.com/elastic/ecs
+
+## Install
+
+`go get github.com/andrewkroh/go-ecs@main`
+
+## Usage
+
+```go
+package main
+
+import (
+	"fmt"
+
+	"github.com/andrewkroh/go-ecs"
+)
+
+func main() {
+	field, err := ecs.Lookup("host.os.name", "8.10")
+	if err != nil {
+		return err
+	}
+
+	fmt.Println("data_type", field.DataType)
+	fmt.Println("is array", field.Array)
+	fmt.Println("pattern", field.Pattern)
+	fmt.Println("description", field.Description)
+}
+```

ecs_test.go

@@ -17,7 +17,11 @@
 
 package ecs
 
-import "testing"
+import (
+	"encoding/json"
+	"fmt"
+	"testing"
+)
 
 func TestLookup(t *testing.T) {
 	testCases := []struct {
@@ -65,3 +69,20 @@ func BenchmarkLookup(b *testing.B) {
 		}
 	}
 }
+
+func ExampleLookup() {
+	field, err := Lookup("host.os.name", "8.10")
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	data, _ := json.MarshalIndent(field, "", "  ")
+	fmt.Printf("%s", data)
+	// Output: {
+	//   "name": "host.os.name",
+	//   "data_type": "keyword",
+	//   "array": false,
+	//   "description": "Operating system name, without the version."
+	// }
+}

internal/version/field.go

@@ -29,7 +29,7 @@ type Field struct {
 	Array bool `json:"array" yaml:"array"`
 
 	// Regular expression pattern that can be used to validate the value.
-	Pattern string `json:"pattern" yaml:"pattern"`
+	Pattern string `json:"pattern,omitempty" yaml:"pattern,omitempty"`
 
 	// Short description of the field.
 	Description string `json:"description" yaml:"description"`