Add instructions for build

BUILD_INSTRUCTIONS.md

+# Building the lib
+
+The following procedure has been written for Ubuntu 22.04 OS.
+
+
+Install the dependencies :
+
+```
+./prepare_build.sh
+```
+
+## Building librealsense
+
+Clone the repository : 
+
+```
+git clone https://github.com/IntelRealSense/librealsense.git
+```
+
+
+Create the build directory and prepare the build 
+
+```
+cd librealsense
+mkdir build && cd build
+cmake ../
+make
+```
+
+Once built, install the lib :
+
+```
+make install
+```
+
+
+##  Building lib sandbox
+
+Clone the repository (and checkout to the opencv4 branch)
+
+```
+git clone ssh://git@ssh.hesge.ch:10572/ar_sandbox/ar_sandbox_lib.git
+git checkout opencv4
+```
+
+Build the lib:
+
+```
+make all
+```
\ No newline at end of file

Prereqs.sh

+
+ln -s /usr/include/opencv4/opencv2 /usr/include/opencv2
+cd /usr/lib/x86_64-linux-gnu/pkgconfig
+ln -s opencv4.pc opencv.pc
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prepare_build.sh

+NC='\033[0m' # No Color
+GRE='\033[0;32m'
+BLU='\033[0;34m'
+YEL='\033[0;33m'
+
+
+echo "${BLU}========================================"
+echo "=   libsandbox requirements install    ="
+echo "========================================${NC}"
+
+echo "${YEL}Updating APT cache${NC}"
+apt update
+
+echo "${BLU}========================================"
+echo "=   librealsense build requirements    ="
+echo "========================================${NC}"
+apt install -y git wget cmake build-essential libssl-dev libusb-1.0-0-dev libudev-dev pkg-config libgtk-3-dev libglfw3-dev libgl1-mesa-dev libglu1-mesa-dev at v4l-utils
+
+echo "${BLU}========================================"
+echo "=    libsandbox build requirements     ="
+echo "========================================${NC}"
+apt install -y libyaml-cpp-dev libopencv-dev qtbase5-dev qttools5-dev
+
+echo "${BLU}========================================"
+echo "=  Linking opencv4/opencv2 to opencv2  ="
+echo "========================================${NC}"
+ln -s /usr/include/opencv4/opencv2 /usr/include/opencv2
+echo "${BLU}========================================"
+echo "=  Linking opencv4.pc to opencv.pc  ="
+echo "========================================${NC}"
+ln -s /usr/lib/x86_64-linux-gnu/pkgconfig/opencv4.pc /usr/lib/x86_64-linux-gnu/pkgconfig/opencv.pc
+echo "${GRE}Successfuly prepared environment${NC}"
\ No newline at end of file