Add warning re. different versions of mean shift algorithm

README.md

@@ -70,6 +70,10 @@ version of the mean shift grouping algorithm with:
     cd LSMTool
     python setup.py install --build_c_extentions
 
+Note that the C++ version will give slightly different results compared to the
+Python version, but such differences are not expected to be important
+in practice.
+
 ### Testing
 
 You can test that the installation worked with: