docs: mention Makefile task for non-free contrib modules

Signed-off-by: Ron Evans <[email protected]>
rahulbasu · Mar 13, 2019 · a897c36 · a897c36
1 parent 870e678
commit a897c36
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/contrib/README.md b/contrib/README.md
@@ -27,3 +27,5 @@ Then you will be able to use the functions within the `contrib` subpackage. For
 si := contrib.NewSIFT()
 kp := si.Detect(img)
 ```
+
+Note that some of the features in this package require building OpenCV with the `OPENCV_ENABLE_NONFREE=ON` option. You can run `make build_nonfree` to build with this option.