added card information do the doc

The cards haven't been merged to the trunk, but where not available in the doc. I personally found the feature just because i was reading the css.

it was just a copy paste

README.md

@@ -125,6 +125,50 @@ The syntax to add a Material icon is:
 
      <i class="icon icon-material-favorite"></i>
 
+### Cards 
+
+A card will expand to fill all of the available width (e.g. column's width). Card's height will be automatically resized to match width.
+
+Here is an example on how to use it:
+
+    <div class="card">
+
+        <div class="card-height-indicator"></div>
+
+        <div class="card-content">
+
+            <div class="card-image">
+                <img src="./image.jpg" alt="Loading image...">
+                <h3 class="card-image-headline">Lorem Ipsum Dolor</h3>
+            </div>
+
+            <div class="card-body">
+                <p>Lorem Ipsum is simply dummy text of the printing and typesetting industry.</p>
+            </div>
+
+            <footer class="card-footer">
+                <button class="btn btn-flat">Share</button>
+                <button class="btn btn-flat btn-warning">Learn More</button>
+            </footer>
+
+        </div>
+
+    </div>
+Cards will adapt to column's width. The card below will have width equal to col-lg-6:
+
+    <div class="row">
+        <div class="col-lg-3"></div>
+
+        <div class="col-lg-6">
+            <div class="card">
+                ...
+            </div>
+        </div>
+
+        <div class="col-lg-3"></div>
+    </div>
+
+
 ## Material.js
 
 `Material.js` is a jQuery plugin that adds some magic to your markup and allows Material Design for Bootstrap to style some elements like inputs, checkboxes, radios etc.