docs: comment and example for InputInfo.Env

Author: steverusso

builder.go

@@ -279,6 +279,8 @@ func (in InputInfo) Help(blurb string) InputInfo {
 	return in
 }
 
+// Env sets the name of the environment variable for this InputInfo. The parser will parse
+// the value of that environment variable for this input if it is set.
 func (in InputInfo) Env(e string) InputInfo {
 	in.EnvVar = e
 	return in

examples_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"image"
 	"net/url"
+	"os"
 	"strconv"
 	"strings"
 	"time"
@@ -99,6 +100,18 @@ func ExampleInputInfo_WithParser() {
 	// image.Point{X:3, Y:7}
 }
 
+func ExampleInputInfo_Env() {
+	os.Setenv("FLAG", "hello")
+
+	c := cli.New().
+		Opt(cli.NewOpt("flag").Env("FLAG")).
+		ParseOrExit([]string{}...)
+
+	fmt.Println(cli.Get[string](c, "flag"))
+	// Output:
+	// hello
+}
+
 func ExampleInputInfo_Long() {
 	in := cli.New("example").
 		Help("example program").