sayantani11: Doc about Persistent disk added

JobBuild
446
11-02 13:08
pull-cluster-api-provider-gcp-build 1466801445478076416
pull-cluster-api-provider-gcp-e2e-test 1466801445578739712
pull-cluster-api-provider-gcp-make 1466801445507436544
pull-cluster-api-provider-gcp-test 1466801445444521984
pull-cluster-api-provider-gcp-verify 1466801445540990976 1456964664368828416 1455522103297052672