doc(Tutorial): Add explanation for app config (#4137)

[oktak]

What do these changes do?

Documentation on Tutorial section, about explanation on why aiohttp chooses to store configurations in one place(the main app).

Are there changes in behavior for the user?

No.

Related issue number

#4137

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the pr
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."

[asvetlov]

@Arfey please take a look.
I suspect that we should close the PR with 'invalid' label.
Yet another catcher of Hacktoberfest T-Shirts

[Arfey]

@asvetlov i believe that we'll make with that MR something helpful 😀
I think this is the first place where they quote me 😅

[Arfey]

@oktak thx for your contribution.

I'm not sure that it's what actually we need. But we can improve that.

1. We don't need to create a new stage of documentation. Instead of that the better way will be add this information in place where is this used for the first time. I found this place.
2. We can use Note block for that.
3. Save all configuration and connection it's just convention (but best practice). We need so easy and shot explain why we need to use this approach and what benefits we get.

[Arfey]

@asvetlov may be u will put here a list of some things which u want to show in this part of documentation.

As example:

• this is helpful when you want to share your setting between subapp because ...

Of course, if you'll a free time.

[asvetlov]

You are the author of #4137, not me.
I appreciate any docs improvement and happy to review but I have no such list of proposals in my memory.

[oktak]

@asvetlov , I disagree that you simply close the PR with 'invalid' label without stating more specific requirement that like @Arfey does.

True that I am aiming for T-shirt. But, I don't think my pull request is totally useless. I am actually want to help to tackle the issue #4137 . And I did a few research, and discuss with the issue opener. I tried to guess what end-product actually they want. I clone the repo and, build the docs, add the page.

If anyone does not welcome Hacktoberfest joiner, please do not add Hacktoberfest labels in all their issues.

Aiohttp is a nice project, I love to use it. So I choose to help.

[asvetlov]

@oktak you've created tutorial/index.rst
If you open http://docs.aiohttp.org/en/stable/web.html you'll see that aiohttp tutorial already exists, it is hosted on separate https://github.com/aio-libs/aiohttp-demos repository

Your PR looks so... incomplete; I've thought that it has no intention to be merged.

[oktak]

@asvetlov Thank you for your clarification. I am clearer now.
I know there exists the tutorial page, and tried re-confirm it:
#4137 (comment)

It turns out I'd better find my way to contribute on the separated https://github.com/aio-libs/aiohttp-demos repository, rather than this main repository. With the review comments, I think I could make more complete PR.

I suggest your team also close issue #4137 or add an invalid label to it as well, and then open new issue on demos repository.