Add style and help button.

frontend/src/app/pages/publication-edition/publication-edition.component.html

@@ -47,6 +47,9 @@
                             <button type="button" disabled matTooltip="Click to insert a code block">
                                 <mat-icon>code</mat-icon>
                             </button>
+                            <button type="button" disabled matTooltip="Click to display editor help">
+                                <mat-icon>help</mat-icon>
+                            </button>
                         </div>
                         <mat-form-field class="example-form-field">
                             <mat-label>Content</mat-label>