website: update push docs

website/source/docs/commands/push.html.markdown

@@ -52,10 +52,20 @@ The command-line flags are all optional. The list of available flags are:
 
 * `-no-color` - Disables output with coloring
 
+
+* `-set=foo` - Marks a specific variable to be updated within Atlas.
+  Normally, if a variable is already set in Atlas, Terraform will not
+  send the local value (even if it is different). This forces it to
+  send the local value to Atlas. This flag can be repeated multiple times.
+
 * `-token=<token>` - Atlas API token to use to authorize the upload.
   If blank or unspecified, the `ATLAS_TOKEN` environmental variable
   will be used.
 
+* `-var='foo=bar'` - Set the value of a variable for the Terraform configuration.
+
+* `-var-file=foo` - Set the value of variables using a variable file.
+
 * `-vcs=true` - If true (default), then Terraform will detect if a VCS
   is in use, such as Git, and will only upload files that are comitted to
   version control. If no version control system is detected, Terraform will
@@ -78,6 +88,20 @@ all the files to be safe. To exclude certain files, specify the `-exclude`
 flag when pushing, or specify the `exclude` parameter in the
 [Atlas configuration section](/docs/configuration/atlas.html).
 
+## Terraform Variables
+
+When you `push`, Terraform will automatically set the local values of
+your Terraform variables within Atlas. The values are only set if they
+don't already exist within Atlas. If you want to force push a certain
+variable value to update it, use the `-set` flag.
+
+All the variable values stored within Atlas are encrypted and secured
+using [Vault](https://vaultproject.io). We blogged about the
+[architecture of our secure storage system](https://hashicorp.com/blog/how-atlas-uses-vault-for-managing-secrets.html) if you want more detail.
+
+The variable values can be updated using the `-set` flag or via
+the [Atlas website](https://atlas.hashicorp.com).
+
 ## Remote State Requirement
 
 `terraform push` requires that