indicate that user should run tbbvars for FindTBB

BUILD.md

@@ -5,6 +5,7 @@ Dependencies
 * [glm](http://glm.g-truc.net/0.9.5/index.html) ~> 0.9.5.2
 * [OpenSSL](https://www.openssl.org/related/binaries.html) ~> 1.0.1g
   * IMPORTANT: OpenSSL 1.0.1g is critical to avoid a security vulnerability.
+* [Intel Threading Building Blocks](https://www.threadingbuildingblocks.org/) ~> 4.3
 
 #####Linux only
 * [freeglut](http://freeglut.sourceforge.net/) ~> 2.8.0
@@ -67,7 +68,7 @@ Should you choose not to install Qt5 via a package manager that handles dependen
 [Homebrew](http://brew.sh/) is an excellent package manager for OS X. It makes install of all hifi dependencies very simple.
 
     brew tap highfidelity/homebrew-formulas
-    brew install cmake glm openssl
+    brew install cmake glm openssl tbb
     brew install highfidelity/formulas/qt5
     brew link qt5 --force
 
@@ -173,6 +174,9 @@ The recommended route for CMake to find the external dependencies is to place al
             -> bin
             -> include
             -> lib
+        -> tbb
+            -> include
+            -> lib
         -> zlib
            -> include
            -> lib
@@ -202,6 +206,12 @@ To prevent these problems, install OpenSSL yourself. Download the following bina
 
 Install OpenSSL into the Windows system directory, to make sure that QT uses the version that you've just installed, and not some other version.
 
+#### Intel Threading Building Blocks (TBB)
+
+Download the stable release for Windows from the [Intel Threading Building Blocks website](https://www.threadingbuildingblocks.org/). By default, TBB will install to Program Files. You may also choose to install it to %HIFI_LIB_DIR%\TBB. 
+
+You must run `tbbvars.bat` so that the find module included with this project will be able to find TBB no matter where you installed it. `tbbvars.bat` is located in the 'bin' folder of your TBB install. For a default installation on a 64-bit architechture, tbbvars can be found at `C:/Program Files (x86)/Intel/TBB/bin/tbbvars.bat`.
+
 #### Zlib
 
 Download the compiled DLL from the [zlib website](http://www.zlib.net/). Extract to %HIFI_LIB_DIR%\zlib.