Add admin dashboard widgets for each .md file found in theme root.

theme-widget-documents.php

<?php
/**
 * Add admin dashboard widgets for each .md file found in theme root.
 *
 * reads the *.md markdown files at the root of the theme and display a widget for each .md in the admin dashboard
 * <!> Requires the class Parsedown https://github.com/erusev/parsedown
 * <!> includes classes/Parsedown.php
 */
add_action('wp_dashboard_setup', function(){
    $themeDir = get_template_directory();
    $markdownFiles = glob($themeDir.'/*.md');

    // Is there any .md files ?
    if (!empty($markdownFiles)) {
        include $themeDir.'/classes/Parsedown.php';
        $Parsedown = new Parsedown();

        // Add a widget for each .md file found
        foreach ($markdownFiles as $k => $file) {
            wp_add_dashboard_widget(
                'website_documentation_'.$k, //slug
                str_replace('.md', '', ucfirst(basename($file))), //name
                function() use ($file, $Parsedown) { //content
                    $text = file_get_contents($file);
                    echo $Parsedown->text($text);
                }
            );
        }
    }
});