Add `markdownlint` linter and fix issues. Config is based on the one
from electron's repo with a few rules relaxed.

Adds an upgrade script that automates upgrading installations on Linux from binary releases, so people don't need to reinvent the wheel. Hopefully this leads to less questions about how to upgrade, and consequently less Gitea instances running unmaintained versions in the wild.

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Gusted <williamzijl7@hotmail.com>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>

* doc: Upgrade from an old Gitea

* update backup steps

* Update docs/content/doc/upgrade/from-gitea.en-us.md

Co-authored-by: delvh <dev.lh@web.de>

* Update docs/content/doc/upgrade/from-gitea.en-us.md

Co-authored-by: delvh <dev.lh@web.de>

* Update docs/content/doc/upgrade/from-gitea.en-us.md

Co-authored-by: delvh <dev.lh@web.de>

* Update docs/content/doc/upgrade/from-gitea.en-us.md

Co-authored-by: delvh <dev.lh@web.de>

* Update docs/content/doc/upgrade/from-gitea.en-us.md

Co-authored-by: delvh <dev.lh@web.de>

* Update docs/content/doc/upgrade/from-gitea.en-us.md

Co-authored-by: delvh <dev.lh@web.de>

* Update docs/content/doc/upgrade/from-gitea.en-us.md

Co-authored-by: delvh <dev.lh@web.de>

* update backup tips

* update table header

* Update docs/content/doc/upgrade/from-gitea.en-us.md

Co-authored-by: silverwind <me@silverwind.io>

* Update docs/content/doc/upgrade/from-gitea.en-us.md

Co-authored-by: silverwind <me@silverwind.io>

* Update docs/content/doc/upgrade/from-gitea.en-us.md

Co-authored-by: techknowlogick <matti@mdranta.net>

* Update docs/content/doc/upgrade/from-gitea.en-us.md

Co-authored-by: techknowlogick <matti@mdranta.net>

* Update from-gitea.en-us.md

* Update from-gitea.en-us.md

* Update from-gitea.en-us.md

* Update from-gitea.en-us.md

* Update from-gitea.en-us.md

* Update from-gitea.en-us.md

* Update from-gitea.en-us.md

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: techknowlogick <matti@mdranta.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lauris BH <lauris@nix.lv>

* align "make help"

* format

* untouch build/generate-svg.js

* untouch .eslintrc

* combine editorconfig's

* rm editorconfig

Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

* Remove migration support from versions earlier than 1.6.0

* Remove unused functions

* Update gogs upgrade instructions

* Improve "latest" link as per @jolheiser

Co-authored-by: Antoine GIRARD <sapk@users.noreply.github.com>
Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

Signed-off-by: kolaente <k@knt.li>

The link without slash is not working

* Add docs about database migration

* Reorder upgrade from Gogs steps

* Update "Upgrade from Gogs" en-us doc

- Move "Change gogs specific information" FROM/TO steps up
  to just beneath matching section header, adjust indention
  and explicitly specify syntax of code sample to provide
  highlighting

- Adjust header levels to match what appears to be the
  intended level, remove trailing decoration (see below)

- Move "Upgrading to most recent ..." section down, remove
  decoration (section header formatting likely covers this
  well enough already)

refs go-gitea/gitea#4286, go-gitea/gitea#3558

* Update "Upgrade from Gogs" fr-fr doc

- Adjust indention and explicitly specify syntax of code
  sample to provide highlighting

- Adjust header levels to match what appears to be the
  intended level, remove trailing decoration since
  section header formatting likely covers this
  well enough already

refs go-gitea/gitea#4286, go-gitea/gitea#3558

Updates the manual for latest gogs changes.

* Clean up spelling, grammar, perspective, whitespace, language, markup, etc.

original PR go-gitea/docs#147 and author @0xbaadf00d

* import docs into main repository

Signed-off-by: Matti Ranta <matti@mdranta.net>