update script and add more comments

build.sh

@@ -1,6 +1,49 @@
-#!/bin/sh
-git submodule update --init
-mkdir build
-cd build
-cmake ..
-make
+#!/bin/bash
+
+#building drogon
+function build_drogon() {
+
+    #update the submodule and initialize
+    git submodule update --init
+    
+    #saving current directory
+    current_dir="${PWD}"
+
+    #the folder we will build
+    build_dir='./build'
+    if [ -d $build_dir ]; then
+        echo "Deleted folder: ${build_dir}"
+        rm -rf build
+    fi
+
+    #creating building folder
+    echo "Created building folder: ${build_dir}"
+    mkdir build
+
+    echo "Entering folder: ${build_dir}"
+    cd $build_dir
+
+    echo "Start building drogon ..."
+    cmake ..
+    
+    #errors exit
+    if [ "$?" != "0" ]; then
+        exit
+    fi
+    
+    make
+    
+    #errors exit
+    if [ "$?" != "0" ]; then
+        exit
+    fi
+
+    echo "Installing header files ..."
+    sudo make install
+
+    #reback current directory
+    cd $current_dir
+    #ok!
+}
+
+build_drogon