Update documentation-style-guide.md (#32690)

contribute/style-guides/documentation-style-guide.md

@@ -14,7 +14,7 @@ The *Documentation style guide* is a living document. Add to it whenever a style
 
 ## Published guides
 
-For all items that are not covered in this guide, refer to the [Microsoft Style Guide](https://docs.microsoft.com/en-us/style-guide/welcome/) and the [Chicago Manual of Style](https://www.chicagomanualofstyle.org/home.html).
+For all items that are not covered in this guide, refer to the [Google developer documentation style guide](https://developers.google.com/style) and the [Microsoft style guide](https://docs.microsoft.com/en-us/style-guide/welcome/), in that order.
 
 ## Spelling
 
@@ -287,6 +287,15 @@ Do not hyphenate when used as an adjective unless the lack of hyphen would cause
 
 Do not hyphenate when it is used as a noun. For example: _Open source is the best way to develop software._
 
+#### plugin, plug in
+
+Two words if used as a verb, one word if used as a noun. Do not use _plug-in_.
+
+**Examples**
+
+- Plug in the appliance.
+- Download the plugin.
+
 #### setup, set up
 
 Two words if used as a verb, one word if used as a noun.
@@ -296,7 +305,7 @@ Two words if used as a verb, one word if used as a noun.
 - Set up the workspace.
 - Initial setup might take five minutes.
 
-### node_exporter, windows_exporter
+#### node_exporter, windows_exporter
 
 When referencing the Prometheus data source exporters, always use "node_exporter" and "windows_exporter" when referring to those tools.