doc: documentation is now in the same repository as the code

Demo site will be generated in subfolder /demo

docs/config/site.md

@@ -0,0 +1,40 @@
+# Site-wide settings
+
+Fields under `[Params]`:
+
+## description
+
+- Type: `string`
+
+Site description. By default, it falls back to `.Params.Sidebar.Subtitle`.
+
+## mainSections
+
+- Type: `[string]`
+- Default: `["post"]`
+
+Pages places under this/those sections will be shown on homepage and archive page.
+
+For more information, take a look at Hugo's documentation on [Content Sections](https://gohugo.io/content-management/sections/).
+
+## featuredImageField
+
+- Type: `string`
+- Default: `image`
+
+Front Matter **field** used to get the featured image of a page. 
+
+## rssFullContent
+
+- Type: `bool`
+- Default: `true`
+
+Output page's full content in RSS.
+
+## favicon
+
+- Type: `string`
+
+Site favicon path. 
+
+For example, if you want to use the favicon in `static/favicon.ico`, set `favicon` to `/favicon.ico`.