Add Upgrading into README

kubectl create -f csi-s3.yaml

```

If you're upgrading from a previous version which had `attacher.yaml` you

can safely delete all resources created from that file:

##### Upgrading

If you're upgrading from <= 0.35.5 - delete all resources from `attacher.yaml`:

```

wget https://raw.githubusercontent.com/yandex-cloud/k8s-csi-s3/v0.35.5/deploy/kubernetes/attacher.yaml

kubectl delete -f attacher.yaml

```

If you're upgrading from <= 0.40.6 - delete all resources from old `provisioner.yaml`:

```bash

wget -O old-provisioner.yaml https://raw.githubusercontent.com/yandex-cloud/k8s-csi-s3/v0.40.6/deploy/kubernetes/provisioner.yaml

kubectl delete -f old-provisioner.yaml

```

Then reapply `csi-s3.yaml`, `driver.yaml` and `provisioner.yaml`:

```bash

cd deploy/kubernetes

kubectl apply -f provisioner.yaml

kubectl apply -f driver.yaml

kubectl apply -f csi-s3.yaml

```

#### 3. Create the storage class

```bash