Merge pull request docker#945 from londoncalling/d4mac-requirements

clarify Docker for Mac OS requirements

Author: londoncalling

docker-for-mac/index.md

@@ -53,11 +53,11 @@ For more about stable and beta channels, see the
 
 >**Important Notes**:
 >
->- Docker for Mac requires macOS 10.10.3 Yosemite or newer running on a 2010 or
->    newer Mac, with Intel's  hardware support for MMU virtualization. Please see
->    [What to know before you install](index.md#what-to-know-before-you-install)
->    for a full list of prerequisites.
->
+>- Docker for Mac requires OS X El Capitan 10.11 or newer macOS release running on a 2010 or
+    newer Mac, with Intel's  hardware support for MMU virtualization. The app will run on 10.10.3 Yosemite, but with limited support. Please see
+    [What to know before you install](index.md#what-to-know-before-you-install)
+    for a full explanation and list of prerequisites.
+
 >- You can switch between beta and stable versions, but you must have only one
 >    app installed at a time. Also, you will need to save images and export
 >    containers you want to keep before uninstalling the current version before