mention rows must be in containers in grid docs

css.html

@@ -75,6 +75,7 @@ base_url: "../"
     <h3 id="grid-intro">Introduction</h3>
     <p>Grid systems are used for creating page layouts through a series of rows and columns that house your content. Here's how the Bootstrap grid system works:</p>
     <ul>
+      <li>Rows must be placed within a <code>.container</code> for proper alignment and padding.</li>
       <li>Use rows to create horizontal groups of columns.</li>
       <li>Content should be placed within columns, and only columns may be immediate children of rows.</li>
       <li>Predefined grid classes like <code>.row</code> and <code>.col-xs-4</code> are available for quickly making grid layouts. LESS mixins can also be used for more semantic layouts.</li>