Add tfdoc block to proxy example

networking/filtering-proxy/README.md

@@ -14,3 +14,23 @@ To simplify the usage of the proxy, a Cloud DNS private zone is created and the
 You can optionally deploy the Squid server as [Managed Instance Group](https://cloud.google.com/compute/docs/instance-groups) by setting the `mig` option to `true`. This option defaults to `false` which results in a standalone VM.
 
 ![High-level diagram](squid.png "High-level diagram")
+
+<!-- BEGIN TFDOC -->
+## Variables
+
+| name | description | type | required | default |
+|---|---|:---: |:---:|:---:|
+| billing_account | Billing account id used as default for new projects. | <code title="">string</code> | ✓ |  |
+| prefix | Prefix used for resources that need unique names. | <code title="">string</code> | ✓ |  |
+| region | Default region for resources | <code title="">string</code> | ✓ |  |
+| root_node | Root node for the new hierarchy, either 'organizations/org_id' or 'folders/folder_id'. | <code title="">string</code> | ✓ |  |
+| *cidrs* | CIDR ranges for subnets | <code title="map&#40;string&#41;">map(string)</code> |  | <code title="&#123;&#10;apps  &#61; &#34;10.0.0.0&#47;24&#34;&#10;proxy &#61; &#34;10.0.1.0&#47;28&#34;&#10;&#125;">...</code> |
+| *mig* | Enables the creation of an autoscaling managed instance group of squid instances. | <code title="">bool</code> |  | <code title="">false</code> |
+| *nat_logging* | Enables Cloud NAT logging if not null, value is one of 'ERRORS_ONLY', 'TRANSLATIONS_ONLY', 'ALL'. | <code title="">string</code> |  | <code title="">ERRORS_ONLY</code> |
+
+## Outputs
+
+| name | description | sensitive |
+|---|---|:---:|
+| squid-address | None |  |
+<!-- END TFDOC -->