docs: Update readme

Author: obalunenko

README.md

@@ -8,9 +8,7 @@
 # getenv
 
 Package getenv provides functionality for loading environment variables and parse them into go builtin types.
-
-## Types supported:
-
+Types supported:
 - string
 - []string
 - int
@@ -28,3 +26,93 @@ Package getenv provides functionality for loading environment variables and pars
 - time.Time
 - time.Duration
 - bool
+
+## Examples
+
+### EnvOrDefault
+
+EnvOrDefault retrieves the value of the environment variable named
+by the key.
+If variable not set or value is empty - defaultVal will be returned.
+
+```golang
+package main
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/obalunenko/getenv"
+	"github.com/obalunenko/getenv/option"
+)
+
+func main() {
+	key := "GH_GETENV_TEST"
+
+	defer func() {
+		if err := os.Unsetenv("GH_GETENV_TEST"); err != nil {
+			panic(err)
+		}
+	}()
+
+	var val any
+
+	// string
+	if err := os.Setenv(key, "golly"); err != nil {
+		panic(err)
+	}
+
+	val = getenv.EnvOrDefault(key, "golly")
+	fmt.Printf("[%T]: %v\n", val, val)
+
+	// int
+	if err := os.Setenv(key, "123"); err != nil {
+		panic(err)
+	}
+
+	val = getenv.EnvOrDefault(key, -99)
+	fmt.Printf("[%T]: %v\n", val, val)
+
+	// time.Time
+	if err := os.Setenv(key, "2022-01-20"); err != nil {
+		panic(err)
+	}
+
+	val = getenv.EnvOrDefault(key,
+		time.Date(1992, 12, 1, 0, 0, 0, 0, time.UTC),
+		option.WithTimeLayout("2006-01-02"),
+	)
+	fmt.Printf("[%T]: %v\n", val, val)
+
+	// []float64
+	if err := os.Setenv(key, "26.89,0.67"); err != nil {
+		panic(err)
+	}
+
+	val = getenv.EnvOrDefault(key, []float64{-99},
+		option.WithSeparator(","),
+	)
+	fmt.Printf("[%T]: %v\n", val, val)
+
+	// time.Duration
+	if err := os.Setenv(key, "2h35m"); err != nil {
+		panic(err)
+	}
+
+	val = getenv.EnvOrDefault(key, time.Second)
+	fmt.Printf("[%T]: %v\n", val, val)
+
+}
+
+```
+
+ Output:
+
+```
+[string]: golly
+[int]: 123
+[time.Time]: 2022-01-20 00:00:00 +0000 UTC
+[[]float64]: [26.89 0.67]
+[time.Duration]: 2h35m0s
+```