website/docs: note sendfile

website/docs/source/layouts/layout.erb

@@ -172,6 +172,7 @@
 								<ul class="sub unstyled">
 									<li<%= sidebar_current("syncedfolder-basic") %>><a href="/v2/synced-folders/basic_usage.html">Basic Usage</a></li>
 									<li<%= sidebar_current("syncedfolder-nfs") %>><a href="/v2/synced-folders/nfs.html">NFS</a></li>
+									<li<%= sidebar_current("syncedfolder-virtualbox") %>><a href="/v2/synced-folders/virtualbox.html">VirtualBox</a></li>
 								</ul>
 								<% end %>
 

website/docs/source/v2/synced-folders/virtualbox.html.md

@@ -0,0 +1,27 @@
+---
+page_title: "VirtualBox Shared Folders - Synced Folders"
+sidebar_current: "syncedfolder-virtualbox"
+---
+
+# VirtualBox
+
+If you're using the VirtualBox [provider](/v2/providers/index.html), then
+VirtualBox shared folders are the default synced folder type. These synced
+folders use the VirtualBox shared folder system to sync file changes from
+the guest to the host and vice versa.
+
+## Caveats
+
+There is a [VirtualBox bug][sendfile bug] related to `sendfile` which can result
+in corrupted or non-updating files. You should deactivate `sendfile` in any
+web servers you may be running.
+
+In Nginx:
+
+    sendfile off;
+
+In Apache:
+
+    EnableSendfile Off
+
+[sendfile bug]: https://github.com/mitchellh/vagrant/issues/351#issuecomment-1339640