docs: explain where are settings for release files

[ForestJohnson]

Just a tiny change to save someone some time while reading the docs. I got lost in the angular code and npm packages trying to reverse engineer it and figure out what setting controlled this file limit:

Eventually I tracked it down from

gitea/options/locale/locale_en-US.ini

Line 2776 in b74a0f9

file_too_big = File size ({{filesize}} MB) exceeds the maximum size of ({{maxFilesize}} MB).

to

gitea/templates/repo/upload.tmpl

Line 11 in b74a0f9

data-file-too-big="{{.i18n.Tr "dropzone.file_too_big"}}"

to

gitea/web_src/js/index.js

Line 1043 in b74a0f9

dictFileTooBig: $dropzone.data('file-too-big'),

to

gitea/web_src/js/features/dropzone.js

Line 3 in b74a0f9

import(/* webpackChunkName: "dropzone" */'dropzone'),

to

https://www.npmjs.com/package/dropzone

and then I realized I can't read 😅, back to

gitea/templates/repo/upload.tmpl

Line 8 in b74a0f9

data-max-size="{{.UploadMaxSize}}"

and quickly solved it from there!!

gitea/modules/upload/upload.go

Line 81 in b74a0f9

ctx.Data["UploadMaxSize"] = setting.Attachment.MaxSize

Yes I know this long path was 90% me failing to read code properly and going on a red herring journey... but point is we should not have to do this in the first place to know how to configure this file upload form 🥺 👉 👈

[wxiaoguang]

Should the section ## Issue and pull request attachments (attachment) be renamed to ## Issue, pull request and release attachments (attachment)?

[delvh]

Should the section ## Issue and pull request attachments (attachment) be renamed to ## Issue, pull request and release attachments (attachment)?

While I generally agree with that, I would maybe not use this attachment duplication, so that the following would be the new title:
## Issue, pull request and release attachments.

[zeripath]

make lgtm work