docs(MarkdownBuilder): add docs

Author: CarloGauss33

README.md

@@ -134,6 +134,14 @@ You can show `Array` or `Hash` values as html lists.
 
 [Read more!](docs/list.md)
 
+#### Markdown
+
+You can render text as markdown.
+
+<img src="./docs/images/markdown-row.png" height="250" />
+
+[Read more!](docs/markdown.md)
+
 ### Inputs
 
 #### Select2 Input

docs/images/markdown-row.png

@@ -0,0 +1,60 @@
+# Markdown
+
+## Markdown Column
+
+Renders text as markdown in the index view.
+
+You just need to use `markdown_column` method.
+
+```ruby
+index do
+  markdown_column :description
+end
+```
+
+## Markdown Row
+
+Renders text as markdown in the show view.
+
+You just need to use `markdown_row` method.
+
+```ruby
+show do
+  attributes_table do
+    markdown_row :description
+  end
+end
+```
+
+## Options
+
+This builder uses [Redcarpet](https://github.com/vmg/redcarpet) to render the text. You can pass any Redcarpet options to it. Using the options `extensions` and `render_options` to modify existing [Redcarpet options](https://github.com/vmg/redcarpet#and-its-like-really-simple-to-use).
+
+```ruby
+index do
+  markdown_column :description, extensions: { footnotes: true }
+end
+
+index do
+  markdown_column :description, render_options: { hard_wrap: true }
+end
+```
+
+### Builder default options
+
+The builder enables the following options by default to provide a plug-and-play experience:
+
+#### Extensions
+``` json
+fenced_code_blocks: true
+no_intra_emphasis: true
+strikethrough: true
+superscript: true
+```
+
+#### Render options
+
+```json
+filter_html: true,
+hard_wrap: true
+```