Merge pull request #400 from reprojection-calibration/readme-fix

Fix opencv example readme section

Author: christian-rauch

README.md

@@ -136,10 +136,9 @@ Note that this library has no external dependencies. Most applications
 will require, at minimum, a method for acquiring images.
 
 See example/opencv_demo.cc for an example of using AprilTag in C++ with OpenCV.
-This example application can be built by executing the following:
+After building the repository you can run the example opencv application with:
 
-    $ cd examples
-    $ make opencv_demo
+    $ ./build/opencv_demo
 
 Image data in a cv::Mat object can be passed to AprilTag without creating
 a deep copy. Simply create an image_u8_t header for the cv::Mat data buffer: