add markdown support for text widgets

pdb-js/src/app/dashboard-page/dashboard/add-text-dialog/add-text-dialog.component.html

@@ -1,6 +1,6 @@
 <style>
   mat-form-field textarea {
-    height: 7em;
+    height: 20em;
   }
 </style>
 <h1 mat-dialog-title>Add Text</h1>
@@ -9,6 +9,7 @@
     <mat-label>Text</mat-label>
     <textarea matInput [(ngModel)]="text" #textElement focus></textarea>
   </mat-form-field>
+  <div>Text field supports <a href="https://spec.commonmark.org/" target="_blank" rel="noopener">Markdown</a>.</div>
 </div>
 <div mat-dialog-actions align="end">
   <button mat-button mat-dialog-close (click)="close()">Cancel</button>