Adds a small note describing BUILD_opencv_world (#12332)

* Added a mall note describing BUILD_opencv_world cmake option to the Installation in Windows tutorial.

* Made slight changes in BUILD_opencv_world documentation.

* Update windows_install.markdown

improved grammar

doc/tutorials/introduction/windows_install/windows_install.markdown

@@ -319,6 +319,7 @@ libraries). If you do not need the support for some of these, you can just freel
         you are concerned about performance, build them and run.
     -   *BUILD_opencv_python* -\> Self-explanatory. Create the binaries to use OpenCV from the
         Python language.
+    -   *BUILD_opencv_world* -\> Generate a single "opencv_world" binary (a shared or static library, depending on *BUILD_SHARED_LIBS*) including all the modules instead of a collection of separate binaries, one binary per module.
 
     Press again the *Configure* button and ensure no errors are reported. If this is the case, you
     can tell CMake to create the project files by pushing the *Generate* button. Go to the build