Added parallel compilation to bindings compilation. (#3173)

* Added parallel compilation to bindings compilation.

Co-authored-by: Hugo Locurcio <[email protected]>

tutorials/plugins/gdnative/gdnative-cpp-example.rst

@@ -131,10 +131,12 @@ below.
 To generate and compile the bindings, use this command (replacing ``<platform>``
 with ``windows``, ``linux`` or ``osx`` depending on your OS):
 
+To speed up compilation, add `-jN` at the end of the SCons command line where `N` is the number of CPU threads you have on your system. The example below uses 4 threads.
+ 
 .. code-block:: none
 
     cd godot-cpp
-    scons platform=<platform> generate_bindings=yes
+    scons platform=<platform> generate_bindings=yes -j4
     cd ..
 
 This step will take a while. When it is completed, you should have static