Update Readme to reflect optional opencv dependency

README.md

@@ -1,13 +1,13 @@
 # Comm
 
 ## Dependencies
-- opencv: not a specific version necessary (tested with >3.2 and >4.3), no opencv_contrib modules needed
+- opencv (optional: enable with -DWITH_OPENCV=On when cmake-ing): not a specific version necessary (tested with >3.2 and >4.3), no opencv_contrib modules needed
 - gcc: toolchain (for Linux and Windows (mingw)) <br/> 
 Note: possibly working with the Visual Studio compiler as is... Build opencv (or use prebuild distributed files) for the OS and compiler you are using.
 
 ## Building
 - Step 0:
-Install Opencv like presented in the [official documentation](https://docs.opencv.org/master/df/d65/tutorial_table_of_content_introduction.html)
+If opencv needed, install Opencv like presented in the [official documentation](https://docs.opencv.org/master/df/d65/tutorial_table_of_content_introduction.html)
 
 - Step 1:
 ```
@@ -17,6 +17,6 @@ cd Comm
 mkdir build-release
 cd build-release
 # if on windows and you're using the gcc (mingw) toolchain add `-G "MinGW Makefiles"` to the command below
-cmake .. -DCMAKE_BUILD_TYPE=Release
+cmake .. -DCMAKE_BUILD_TYPE=Release -DWITH_OPENCV=On
 make
 ```