docs(www): link to plugin README templates from plugins guide (#14856)

* update creating-plugins guide 

update creating-plugins guide to include plugin template link

* move note where file links to README templates

Author: k-conway

docs/contributing/submit-to-plugin-library.md

@@ -8,7 +8,8 @@ In order to add your plugin to the [Plugin Library](/plugins/), you need to:
 
 1.  publish a package to npm (learn how [here](https://docs.npmjs.com/getting-started/publishing-npm-packages)),
 2.  include the [required files](/docs/files-gatsby-looks-for-in-a-plugin/) in your plugin code,
-3.  and **include a `keywords` field** in your plugin's `package.json`, containing `gatsby` and `gatsby-plugin`.
+3.  **include a `keywords` field** in your plugin's `package.json`, containing `gatsby` and `gatsby-plugin`,
+4.  and document your plugin with a README, there are [plugin templates](/contributing/docs-templates/#plugin-readme-template) available to be used as reference.
 
 After doing so, Algolia will take up to 12 hours to add it to the library search index (the exact time necessary is still unknown), and wait for the daily rebuild of https://gatsbyjs.org to automatically include your plugin page to the website. Then, all you have to do is share your wonderful plugin with the community!