docs: fix piped sh usage (#929)

Signed-off-by: Bala.FA <bala@minio.io>

Author: balamurugana

docs/installation.md

@@ -91,7 +91,7 @@ $ kubectl directpv install --openshift
 #### Installing by generating DirectPV manifests
 To install using generated manifests file, run below command
 ```sh
-$ curl -sfL https://github.com/minio/directpv/raw/master/docs/tools/install.sh | sh - apply
+$ curl -sfL https://github.com/minio/directpv/raw/master/docs/tools/install.sh | sh -s - apply
 ```
 
 ## What's next

docs/tools/install.sh

@@ -113,7 +113,7 @@ function check_directcsi_consistency() {
 }
 
 function is_psp_found() {
-    kubectl get --ignore-not-found=true psp directpv-min-io --no-headers -o NAME | grep -q .
+    kubectl get --ignore-not-found=true psp directpv-min-io --no-headers -o NAME 2>/dev/null | grep -q .
 }
 
 function init() {

docs/upgrade.md

@@ -18,7 +18,7 @@ Follow the below steps for an in-place upgrade
 1. Upgrade DirectPV plugin by [this documentation](#upgrade-directpv-plugin).
 2. Run install script with appropriate node-selector, tolerations, and `KUBELET_DIR_PATH` environment variable. Below is an example:
 ```sh
-$ curl -sfL https://github.com/minio/directpv/raw/master/docs/tools/install.sh | sh - apply
+$ curl -sfL https://github.com/minio/directpv/raw/master/docs/tools/install.sh | sh -s - apply
 ```
 
 ### Upgrade legacy DirectCSI CSI driver