Minor contribution guide doc fixes (GoogleCloudPlatform#10869)

docs/content/develop/custom-code.md

@@ -112,7 +112,7 @@ custom_code: !ruby/object:Provider::Terraform::CustomCode
 ```
 
 
-Use `custom_code.decoder` to inject code that modifies the data that will be sent in the API request. This is useful if the API expects the data to be in a significantly different structure than Terraform does - for example, if the API returns the entire object nested under a key, or uses a different name for a field in the response than in the request. The decoder will run _before_ any [`custom_flatten`]({{< ref "#custom_flatten" >}}) code.
+Use `custom_code.decoder` to inject code that modifies the data recieved from an API response. This is useful if the API returns data in a significantly different structure than what Terraform expects - for example, if the API returns the entire object nested under a key, or uses a different name for a field in the response than in the request. The decoder will run _before_ any [`custom_flatten`]({{< ref "#custom_flatten" >}}) code.
 
 The decoder code will be wrapped in a function like:
 

docs/content/develop/field-reference.md

@@ -285,6 +285,16 @@ understand how the resource maps to the underlying API.
   api_name: 'otherFieldName'
 ```
 
+### `url_param_only`
+If true, the field is not sent in the resource body, and the provider does
+not read the field value from the API response. If unset or false, the field
+is sent in the resource body, and the provider reads the field value from the
+API response.
+
+```yaml
+url_param_only: true
+```
+
 ## `Enum` properties
 
 ### `values`