Add indentation README.md

Co-authored-by: Vincent Composieux <vincent.composieux@gmail.com>

README.md

@@ -121,12 +121,11 @@ value := cacheManager.Get(ctx, "my-key")
 
 ```go
 import (
-"github.com/dgraph-io/ristretto"
-"github.com/eko/gocache/lib/v4/cache"
-"github.com/eko/gocache/lib/v4/store"
-ristretto_store "github.com/eko/gocache/store/ristretto/v4"
+	"github.com/dgraph-io/ristretto"
+	"github.com/eko/gocache/lib/v4/cache"
+	"github.com/eko/gocache/lib/v4/store"
+	ristretto_store "github.com/eko/gocache/store/ristretto/v4"
 )
-
 ristrettoCache, err := ristretto.NewCache(&ristretto.Config{
 	NumCounters: 1000,
 	MaxCost: 100,