Update the README to add TensorFlow node

Author: shahmishal

README.md

@@ -2,10 +2,11 @@
 
 [Swift Community-Hosted CI](https://ci-external.swift.org) is an extension of Swift CI that allows the community to add additional platforms. Community members can volunteer to host new platforms and they are responsible for maintaining the host nodes. The maintainer will provide a build preset which will be periodically built on the node. This allows the Swift community to see the impact of changes on a greater range of platforms.
 
-## Current List of Platforms
+## Current List of Nodes
    * Fedora 27
    * ARMv7 for Debian "Stretch"
    * Ubuntu 16.04
+   * Ubuntu 16.04 for TensorFlow
 
 ## Add Nodes