Document using `nproc` instead of hardcoded number of threads (#4476)

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

development/compiling/compiling_for_linuxbsd.rst

@@ -104,6 +104,20 @@ A good rule of thumb for the ``-j`` (*jobs*) flag, is to have at least as many
 threads compiling Godot as you have cores in your CPU, if not one or two more.
 Feel free to add the ``-j`` option to any SCons command you see below.
 
+You can automatically use all available CPU cores with command substitution.
+
+On Linux, you can use ``nproc``:
+
+::
+
+    scons -j$(nproc)
+
+On \*BSD, you can use ``sysctl -n hw.ncpu``:
+
+::
+
+    scons -j$(sysctl -n hw.ncpu)  
+
 .. note::
 
     Prior to Godot 4.0, the Linux/\*BSD target was called ``x11`` instead of