added display headings classes

Author: MuttakinHasib

data/bootstrap-4.json

@@ -130,6 +130,27 @@
              }
           ]
        },
+       {
+          "title": "ডিসপ্লে হেডিংস",
+          "items":[
+             {
+               "definition": "ডিসপ্লে ওয়ান",
+               "code": "<h1 class='display-1'>Display 1</h1>"
+             },
+             {
+               "definition": "ডিসপ্লে টু",
+               "code": "<h1 class='display-2'>Display 2</h1>"
+             },
+             {
+               "definition": "ডিসপ্লে থ্রি",
+               "code": "<h1 class='display-3'>Display 3</h1>"
+             },
+             {
+               "definition": "ডিসপ্লে ফোর",
+               "code": "<h1 class='display-4'>Display 4</h1>"
+             }
+         ]
+       },
        {
           "title":"টেবিল ক্লাস",
           "items":[