Update readme for installation

Author: AntSimi

README.md

@@ -21,7 +21,7 @@ To avoid problems with installation, use of the virtualenv Python virtual enviro
 Then use pip to install all dependencies (numpy, scipy, matplotlib, netCDF4, cython, pyproj, Shapely, ...), e.g.:
 
 ```bash
-pip install cython numpy matplotlib scipy netCDF4 shapely pyproj
+pip install opencv numpy matplotlib scipy netCDF4 shapely pyproj
 ```
 
 Then run the following to install the eddy tracker: