Update writing-custom-providers.html.md

content/source/docs/extend/writing-custom-providers.html.md

@@ -103,6 +103,13 @@ This establishes the main function to produce a valid, executable Go binary. The
 contents of the main function consume Terraform's `plugin` library. This library
 deals with all the communication between Terraform core and the plugin.
 
+The plugin will need to be created as a go module, so you should run the 
+command to initialize the go module.
+
+```shell
+ go mod init terraform-provider-example
+```
+
 Next, build the plugin using the Go toolchain:
 
 ```shell