Updated authentication instruction

Author: wiazur

dotnet/ComputerVision/readme.md

@@ -43,8 +43,7 @@ The projects in this code are quickstarts that show how to use Computer Vision R
 ## Running the samples
 
 1. Right-click on the relavant project (detectObjects, extractText, etc) and click on 'Set as StartUp Project'
-2. In 'Program.cs' , update the line ```public const string subscriptionKey = "<your training key here>";``` with your subscription key. For example, if your subscription key is `0123456789abcdef0123456789ABCDEF`, then the line should look like ``` public const string subscriptionKey = "0123456789abcdef0123456789ABCDEF"; ```
-3. Update the endpoint with the region you generated your endpoint for. For example, if you are using the westcentralus endpoint, you should change the line ``` public const string endpoint = "https://westus.api.cognitive.microsoft.com"; ``` to  ``` public const string endpoint = "https://westcentralus.api.cognitive.microsoft.com"; ```
+2. In 'Program.cs', add your Azure Computer Vision subscription key and endpoint to your environment variables with the variable names: COMPUTER_VISION_SUBSCRIPTION_KEY and COMPUTER_VISION_ENDPOINT.
 4. (Optional) Change the remote image URL and location of local image
 5. (Optional) Comment out visual parameters not needed for AnalyzeImage 
 6. Hit F5 or build the solution