Update install instructions with v1.0.0-beta.1 (#2309)

Author: mortent

site/installation/README.md

@@ -101,7 +101,7 @@ $ kpt version
   https://console.cloud.google.com/gcr/images/kpt-dev/GLOBAL/kpt-gcloud?gcrImageListsize=30
 [cloud-sdk]: https://github.com/GoogleCloudPlatform/cloud-sdk-docker
 [linux]:
-  https://github.com/GoogleContainerTools/kpt/releases/download/v1.0.0-alpha.10/kpt_linux_amd64
+  https://github.com/GoogleContainerTools/kpt/releases/download/v1.0.0-beta.1/kpt_linux_amd64
 [darwin]:
-  https://github.com/GoogleContainerTools/kpt/releases/download/v1.0.0-alpha.10/kpt_darwin_amd64
+  https://github.com/GoogleContainerTools/kpt/releases/download/v1.0.0-beta.1/kpt_darwin_amd64
 [migration guide]: /installation/migration