Update Readme file

Author: Foivos Filippopoulos

README.md

@@ -5,16 +5,21 @@ Snapshots (only the ones created by the service) are deleted when they become ol
 
 ## Usage
 ```
- -interval_secs int
+Usage of /gcp-disk-snapshotter:
+  -interval_secs int
         Interval between snapshots in seconds. Defaults to 43200s = 12h (default 43200)
   -labels string
         (Required) Comma separated list of disk labels in format <name>:<value>
+  -log_level string
+        Log Level, defaults to INFO (default "info")
   -project string
         (Required) GCP Project to use
   -retention_hours int
         Retention Duration in hours. Defaults to 720h = 1 month (default 720)
   -snap_prefix string
         Prefix for created snapshots
+  -watch_interval int
+        Interval between watch cycles in seconds. Defaults to 60s (default 60)
   -zones string
         (Required) Comma separated list of zones where projects disks may live
 ```