style-guide: organize content and update sections; *: fix Markdownlint errors (#12148)

* style-guide: organize content and add contents section

* style-guide: fix general writing section title

* style-guide: fix heading level of help and version commands

* style-guide: fix heading level of see also section

* cleanup: update files

Signed-off-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

* contributing: fix page for markdown lint

Signed-off-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

* fix: markdownlint errors across files

Signed-off-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

* docs: improve documentation about keycaps

Signed-off-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

* docs: add info about optional and string placeholders

Signed-off-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

* cleanup: sync changes with recent versions of style guide

Signed-off-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

* cleanup: update style guide

Co-authored-by: Vítor Henrique <87824454+vitorhcl@users.noreply.github.com>

* docs: update style guide

Co-authored-by: Vítor Henrique <87824454+vitorhcl@users.noreply.github.com>

* docs/style-guide: reword more info links section

Co-authored-by: Vítor Henrique <87824454+vitorhcl@users.noreply.github.com>

---------

Signed-off-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>
Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

LICENSE.md

@@ -1,3 +1,4 @@
+<!-- markdownlint-disable MD041 -->
 Copyright © 2014—present the [tldr-pages team](https://github.com/orgs/tldr-pages/people)
 and [contributors](https://github.com/tldr-pages/tldr/graphs/contributors).