Update README.md

Pathfinder/README.md

@@ -85,7 +85,7 @@ Now, to build the library do the following:
 3. run CMake with the following flags: 
 	* Windows: `cmake .. -G "MinGW Makefiles" -DCMAKE_BUILD_TYPE=RelWithDebInfo`
 	* Linux: `cmake .. -DCMAKE_BUILD_TYPE=RelWithDebInfo`
-4. build the library: `cmake --build .`
+4. build the library: `cmake --build .` or `make -j4` 
 	 If everything worked fine, you should now have the file `libPathfinder.so` or `libPathfinder.dll` in your directory.