revise readme

inputs

@@ -3,5 +3,5 @@
   "{{ project_name }}.new_name": "{{ new_name }}",
   "{{ project_name }}.docker": "registry.cn-shanghai.aliyuncs.com/pgx-docker-registry/sentieon-genomics:v2018.08.01",
   "{{ project_name }}.disk_size": "{{ disk_size }}",
-  "{{ project_name }}.cluster_config": "{{ cluster if cluster != '' else 'OnDemand bcs.sn1ne.large img-ubuntu-vpc' }}"
+  "{{ project_name }}.cluster_config": "OnDemand bcs.sn1ne.large img-ubuntu-vpc"
 }