The code from your Unity tip from 6/13/2017

FolderInspector

using UnityEngine;
using System.Collections;
using UnityEditor;

[CustomEditor(typeof(DefaultAsset), editorForChildClasses: true, isFallback = false)]
public class FolderInspector : Editor
{
    private int m_ContentCount;
    private GUIStyle m_TitleStyle;
    private GUIStyle m_ListStyle;

    public void OnEnable()
    {
        // Get our path
        string assetPath = AssetDatabase.GetAssetPath(target);
        // Find the assets inside 
        string[] assetGUIDs = AssetDatabase.FindAssets("", new[] { assetPath });
        // Save our count
        m_ContentCount = assetGUIDs.Length;
    }

    public override void OnInspectorGUI()
    {
        if(m_TitleStyle == null)
        {
            m_TitleStyle = new GUIStyle(EditorStyles.boldLabel);
            m_TitleStyle.fontSize = 20;
            m_ListStyle = new GUIStyle(GUI.skin.label);
            m_ListStyle.fontSize = 20;
        }

        GUI.enabled = true;
        GUILayout.Label("Super Folder ( ͡° ͜ʖ ͡°)", m_TitleStyle);
        if (targets.Length > 1)
        {
            GUILayout.Label("Content Count: Does not Support Multi Selecting");
        }
        else
        {
            GUILayout.Label("Folder Facts", m_ListStyle);
            GUILayout.Label(" 1) Content Count: " + m_ContentCount.ToString(), m_ListStyle);
            GUILayout.Label(" 2) Is a Folder: true", m_ListStyle);
            GUILayout.Label(" 3) Is having a good day: true", m_ListStyle);
            GUILayout.Label(" 4) Is impressed by #UnityTips: true", m_ListStyle);
        }
     
    }
}