Bring usage docs up to date

Author: spenczar

website/source/intro/getting-started/install.html.markdown

@@ -40,11 +40,16 @@ usage: terraform [--version] [--help] <command> [<args>]
 
 Available commands are:
     apply      Builds or changes infrastructure
+    destroy    Destroy Terraform-managed infrastructure
+    get        Download and install modules for the configuration
     graph      Create a visual graph of Terraform resources
+    init       Initializes Terraform configuration from a module
     output     Read an output from a state file
     plan       Generate and show an execution plan
     refresh    Update local state file against real resources
+    remote     Configure remote state storage
     show       Inspect Terraform state or plan
+    taint      Manually mark a resource for recreation
     version    Prints the Terraform version
 ```