Fix icub-head compile robotology-superbuild

[martinaxgloria]

This PR adds a missing cd build in icub-head robotology-superbuild installation here:

documentation/docs/sw_installation/icub_head_superbuild.md

Lines 42 to 47 in 8c830ee

	## Compile robotology-superbuild
	~~~sh
	cd /usr/local/src/robot/robotology-superbuild
	mkdir build
	cmake -DROBOTOLOGY_USES_GAZEBO:BOOL=OFF -DROBOTOLOGY_ENABLE_ICUB_HEAD:BOOL=ON ..
	make

cc @Nicogene

[pattacini]

Thanks!

[traversaro]

By the way usual OT, but I wanted to write that down. Recently I started using more and the -S -B options of CMake, that have the advantage of automatically creating the build directory. Using those options, the instructions can be simplified to be:

cd /usr/local/src/robot/robotology-superbuild
cmake -S. -Bbuild -DROBOTOLOGY_USES_GAZEBO:BOOL=OFF -DROBOTOLOGY_ENABLE_ICUB_HEAD:BOOL=ON
cmake --build ./build

the nice thing is that with -Bbuild, the build directory is automatically created even it does not exists. I am not saying we should switch to those style (as most users probably they are not familiar with those) but I want to shared this options. Another thing that could help usability (once we drop support for CMake 3.16) is robotology/robotology-superbuild#1615, that would further simplify this to:

cd /usr/local/src/robot/robotology-superbuild
cmake --preset xcub-head
cmake --build ./build

[pattacini]

I'm also fond of using the options -S -B. Some time ago I switched to those in many tutorials, including the grasping sandbox.