Add a complete comment system for minima

[YURLAK]

Hello, developers!👋This is my first PR.

Problem.

Minima has less comment system.And disqus has been deprecated.

How to realize it?

I changed three places.

• Added /includes/comments.html,Delete /includes/disqus_comments.html.
• Added comment settings in _config.yml.
• Changed comment part in _layouts/post.html.

At last

After my changes.Now Giscus,Utterance and Disqus are available now.
I tested it successfully on my blog.
And that's all.Thanks😀

[ashmaroli]

Hello @YURLAK,
First of all, welcome to the world of Open Source Softwares.

Regarding your pull request, I love the idea but would like to leave some feedback nevertheless:

• I would prefer not to reserve a top-level config key for this to avoid conflicts on existing sites. Therefore, I'd prefer {{ site.minima.comments.[NEW_KEY] }} instead of the current {{ site.[NEW_KEY] }}.
• We no longer build the demo site using the master branch. So, adding the config details to _config.yml is not only redundant but additional information to delete for users forking the repository. I suggest you comment out all the comment configuration or move it to the README document.
• For readability reasons, it's better that you wrap the attributes of the HTML script tags.
• Lastly, I think you forgot to include the original Disqus code into the new include file.

[YURLAK]

Hello,@ashmaroli.Thanks for your feedback!According to your feedback,I made some changes.Readability does matter,I updated README.md that deleted some redundancy configuration.

[louisroyer]

Some typographic suggestions.

[louisroyer]

Suggested change

	If you want to add comment system for your site,add the following code to the `README.md` file.If not,skip this part.
	If you want to add comment system for your site, add the following code to the `README.md` file. If not, skip this part.

[louisroyer]

Suggested change

	# You must install giscus github app before use.(https://github.com/apps/giscus)
	# You must install giscus github app before use (https://github.com/apps/giscus).

[ashmaroli]

@YURLAK I thought about this bit more. Continuing from previous feedback:

• Comments are not handled by Jekyll itself so no point in having it as a top-level config key.
  Let's use {{ site.minima.comments_provider }} directly instead.
• Rendering comments during development is not desired as it creates unnecessary discussions on Disqus. Perhaps, the same is true for Giscus and Utterances. Either ways, render comments only in "production".
• The script rendered is easily accessible on provider's website. Therefore, we can avoid performance issues on larger sites by recommending users to copy from provider site (or our README) and hardcode user details as needed. We just provide a means to render desired provider script.
• Additionally, provide a means to disable comments entirely for desired posts (via page.comments).
• No built-in comment support to reduce coupling to third-party code.

So, our _layouts/post.html will have something like:

{% if jekyll.environment == "production" %}
  {% unless page.comments == "disabled" %}
    {% assign comments_provider == site.minima.comments_provider %}
    {% if comments_provider %}
      {% capture provider_filepath %}comments/{{ comments_provider }}.html{% endcapture %}
      {% include {{ provider_filepath }} %}
    {% endif %}
  {% endunless %}
{% endif %}

Then, we document what users need to do, in our README along with the note that build will fail if user does not provide associated include file.