chore(Grid): remove headerRowHeight docs

The headerRowHeight option hasn't done anything for a long time. This
change removes it from the docs and specifies how to alter header height
with CSS.

Closes #3665

Author: c0bra

misc/tutorial/302_custom_header.ngdoc

@@ -2,7 +2,15 @@
 @name Tutorial: 302 Custom Header
 @description
 
-Create a grid almost the same as the most basic one, but with a custom header
+You can specify a custom template for your grid's header with the `headerTemplate` grid option. It will take a url, Angular element, or text string.
+
+If you want to customize the height of the header do it by setting a height on your header cells with CSS:
+
+```javascript
+.grid .ui-grid-header-cell {
+  height: 60px;
+}
+```
 
 @example
 <example module="app">
@@ -17,11 +25,20 @@ Create a grid almost the same as the most basic one, but with a custom header
           { name: 'Frank', title: 'Lowly Developer' }
         ]
       };
+
+      $scope.gridOptions2 = {
+        data: [
+          { name: 'Bob', title: 'CEO' },
+          { name: 'Frank', title: 'Lowly Developer' }
+        ]
+      };
     }]);
   </file>
   <file name="index.html">
     <div ng-controller="MainCtrl">
       <div class="grid" ui-grid="gridOptions"></div>
+      <br>
+      <div class="grid grid2" ui-grid="gridOptions2"></div>
     </div>
   </file>
   <file name="header-template.html">
@@ -32,5 +49,9 @@ Create a grid almost the same as the most basic one, but with a custom header
       width: 500px;
       height: 150px;
     }
+
+    .grid2  .ui-grid-header-cell {
+      height: 60px;
+    }
   </file>
-</example>
+</example>