Update README.md

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README.md

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 # About Rosette for Excel (Beta)
 Rosette for Excel is a product developed by [Basis Technology Corp.](basistech.com) to make the features of the Rosette API available to Excel users without the need to write any of their own code. The Rosette API is a tool for accessing Basis Technology’s natural language processing text analysis services. 
 # How to Install  
+Rosette for Excel is currently for Windows OS only. The current "alpha" release has been tested in Office 2013 on Windows 7 & 8, with broader support on its way for the upcoming official GA release.
 To install, copy both the `rosette.application` file and the folder (titled with the version number) to the same location on your personal computer (or clone the repo to your machine). Run `rosette.application`, which may ask for permission to install the add-in. When you next open Excel you will see Rosette in the ribbon. 
 #Getting Started
 Before you can make any calls with either formulas or the ribbon, you’ll need to add a Rosette API key using the dialog found on the ribbon. Head to [developer.rosette.com](developer.rosette.com) to get your free Rosette API key. Enter your key and check your connection with the Rosette API by clicking Check Key. If a green check appears, you’re good to go! An alternate URL can be specified for On Premise users, but is not required. A more in-depth explanation of how to make API calls can be found [here](UseInfo.md).