Merge pull request #37 from twbs/migration-stub

add stub v3 => v4 migration docs page

docs/migration.md

+---
+layout: page
+title: Migrating to v4.x.x
+---
+
+## Migrating from 3.x.x to 4.0.0
+
+Bootstrap 4 is not backwards compatible with v3.x.x. Use this section as a general guide to upgrading from v3.x.x to v4.0.0. For a broader overview, see [what's new](http://blog.getbootstrap.com/DEAD-LINK-FIX-ME-PLEASE) in the v4.0.0 release announcement.
+
+## Major class changes
+This table shows the style changes between v3.x.x and v4.0.0.
+
+<table>
+  <thead>
+    <tr>
+      <th>Bootstrap 3.x.x</th>
+      <th>Bootstrap 4.0.0</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td></td>
+      <td></td>
+    </tr>
+  </tbody>
+</table>
+
+## What's new
+We've added new components and changed some existing ones. Here are the new or updated styles.
+
+<table>
+  <thead>
+    <tr>
+      <th>Component</th>
+      <th>Description</th>
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td></td>
+      <td></td>
+    </tr>
+  </tbody>
+</table>
+
+## What's removed
+The following components have been removed in v4.0.0.
+
+<table>
+  <thead>
+    <tr>
+      <th>Component</th>
+      <th>Removed from 3.x.x</th>
+      <th>4.0.0 Equivalent</th>    
+    </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td></td>
+      <td></td>
+      <td></td>
+    </tr>
+  </tbody>
+</table>
+
+## Additional notes