Add support for external capture card

Author: datamesh-oss

README.md

@@ -9,6 +9,8 @@ METoolkit is a Unity toolkit for devoloping interactive mixed-reality apps for [
 
 ## What's New
 
+METoolkit now supports external capture card, specifically the [BlackMagic Intensity capture card](https://www.blackmagicdesign.com/products/intensity).
+
 Now Unity 2017 is supported by METoolkit from release version v2.3.0. The legacy support for Unity 5.5 is moved to another branch '**[METoolkit_2.2_ForUnity5.5.1](https://github.com/DataMesh-OpenSource/METoolkit/tree/METoolkit_2.2_ForUnity5.5.1)**'. **The master branch is only compatible with Unity 2017.** We recommend Unity 2017 when starting a new project.
 
 ## Components