add page on docs contribution (#1283)

Author: thisisjofrank

runtime/_data.ts

@@ -205,6 +205,7 @@ export const sidebar = [
           "/runtime/contributing/release_schedule/",
           "/runtime/contributing/style_guide/",
           "/runtime/contributing/web_platform_tests/",
+          "/runtime/contributing/docs/",
           "/runtime/contributing/examples/",
         ],
       },

runtime/contributing/docs.md

@@ -0,0 +1,22 @@
+---
+title: "Deno documentation"
+---
+
+We welcome and appreciate contributions to the Deno documentation. If you find
+an issue, or want to add to the docs, each page has an "Edit this page" button
+at the bottom of the page. Clicking this button will take you to the source file
+for that page in the [Deno docs repository](https://github.com/denoland/docs/).
+You can then make your changes and submit a pull request.
+
+Some pages in the Deno documentation are generated from source files in the Deno
+repository. These pages are not directly editable:
+
+- The [API reference](/api/deno/) pages are generated from type definitions in
+  the Deno repository.
+- The [CLI reference](/runtime/reference/cli/) pages for each individual command
+  are generated from source files in the Deno repository.
+
+If you find an issue with one of these pages, you can either submit a pull
+request to the Deno repository. Or raise an issue in the
+[Deno docs repository](https://github.com/denoland/docs/issues) and we'll get it
+fixed.