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>

.markdownlint.json

@@ -0,0 +1,11 @@
+{
+  "default": true,
+  "MD003": { "style": "atx" },
+  "MD007": { "indent": 4 },
+  "MD013": { "line_length": 250 },
+  "MD029": false,
+  "MD033": false,
+  "MD034": false,
+  "no-hard-tabs": false,
+  "whitespace": false
+}