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

Demo site will be generated in subfolder /demo

docs/config/comments.md

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+# Comments
+
+Comment system is a very important part of a blog. It allows readers to express their opinions and thoughts about the post. It also allows the author to interact with the readers.
+
+Stack currently supports the following comment systems:
+
+- [Cactus](https://cactus.chat/)
+- [Cusdis](https://cusdis.com/)
+- [Disqus](https://disqus.com/)
+- [DisqusJS](https://github.com/SukkaW/DisqusJS)
+- [Giscus](https://giscus.app/)
+- [Gitalk](https://github.com/gitalk/gitalk)
+- [Remark42](https://remark42.com/)
+- [Twikoo](https://twikoo.js.org/)
+- [utterances](https://utteranc.es/)
+- [Vssue](https://vssue.js.org/)
+- [Waline](https://waline.js.org/)
+
+Each comment system has its own configuration options placed under `[Params.Comments.COMMENT_SYSTEM]` section. 
+
+For example, utterances's configuration options are placed under `[Params.Comments.utterances]` section.
+
+::: tip
+A full list of supported configuration options can be found in [here](https://github.com/CaiJimmy/hugo-theme-stack/blob/master/config.yaml#L38)
+
+For more information about the meaning of each configuration option, please refer to the documentation of the comment system.
+:::
+
+::: warning
+In case of Disqus, the only configuration option is `disqusShortname`, which is not available at `[Params.Comments.disqus]` section. Instead, it is placed at root section of configuration file.
+:::
+
+## enabled
+
+- Type: `bool`
+- Default: `false`
+
+Enable / disable comment system.
+
+## provider
+
+- Type: `string`
+
+Comment system provider. Possible values are:
+
+- `cactus`
+- `cusdis`
+- `disqus`
+- `disqusjs`
+- `giscus`
+- `gitalk`
+- `remark42`
+- `twikoo`
+- `utterances`
+- `vssue`
+- `waline`