add: Added environment construction documents and README

docs/Build.md

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+## Preparing the development environment
+
+### Task list
+- Building a pure GCC cross-compilation toolchain (i686-elf), not bundled with the system.
+- Building/Installing Bochs and QEMU.
+
+### Compiling i686-elf-gcc
+Open the terminal and execute the [gcc-build.sh](gcc-build.sh) script; this may take about half an hour.
+```sh=
+bash ./gcc-build.sh
+```
+**Permanently add the newly compiled GCC to the PATH environment variable**
+
+Permanently add the newly compiled GCC to the PATH environment variable. The configuration file depends on the shell you are using, such as `${HOME}/.zshrc` for zsh or `${HOME}/.bashrc` for bash. Alternatively, you can directly modify the global `/etc/profile` file (though it's not recommended). Afterward, reboot your system.
+```sh=
+vim ~/.bashrc
+source ~/.bashrc
+```
+Add `export PATH="$HOME/cross-compiler/bin:$PATH"`
+
+**Test the command**
+```sh=
+i686-elf-gcc --version
+```
+output
+```sh=
+i686-elf-gcc (GCC) 11.2.0
+Copyright (C) 2021 Free Software Foundation, Inc.
+This is free software; see the source for copying conditions.  There is NO
+warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+```
+### Compiling Bochs
+Download the [source code](https://sourceforge.net/projects/bochs/files/bochs/2.8/), extract it, and place the [bochs-build.sh](bochs-build.sh) script in the folder. Then, execute the script in the current folder.
+```sh=
+sudo apt install libx11-dev xserver-xorg-dev xorg-dev -y
+sudo apt install libsdl2-dev -y
+sudo apt install libncurses5-dev -y
+sudo apt install xorriso -y
+sudo apt install mtools -y
+sudo apt install qemu-system-i386 -y
+bash ./bochs-build.sh
+```
+**Test the command**
+```sh=
+bochs
+```
+output
+```sh=
+========================================================================
+                        Bochs x86 Emulator 2.7
+              Built from SVN snapshot on August  1, 2021
+                Timestamp: Sun Aug  1 10:07:00 CEST 2021
+========================================================================
+00000000000i[      ] BXSHARE not set. using compile time default '/usr/local/share/bochs'
+------------------------------
+Bochs Configuration: Main Menu
+------------------------------
+
+This is the Bochs Configuration Interface, where you can describe the
+machine that you want to simulate.  Bochs has already searched for a
+configuration file (typically called bochsrc.txt) and loaded it if it
+could be found.  When you are satisfied with the configuration, go
+ahead and start the simulation.
+
+You can also start bochs with the -q option to skip these menus.
+
+1. Restore factory default configuration
+2. Read options from...
+3. Edit options
+4. Save options to...
+5. Restore the Bochs state from...
+6. Begin simulation
+7. Quit now
+
+Please choose one: [2] 7
+
+```
+

scripts/bochs-build.sh

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+export CC=gcc
+export CXX="g++"
+export CFLAGS="-Wall -O2 -fomit-frame-pointer -pipe"
+export CXXFLAGS="$CFLAGS"
+
+(./configure --enable-smp \
+              --enable-cpu-level=6 \
+              --enable-all-optimizations \
+              --enable-x86-64 \
+              --enable-pci \
+              --enable-vmx \
+              --enable-debugger \
+              --enable-disasm \
+              --enable-debugger-gui \
+              --enable-logging \
+              --enable-fpu \
+              --enable-3dnow \
+              --enable-sb16=dummy \
+              --enable-cdrom \
+              --enable-x86-debugger \
+              --enable-iodebug \
+              --disable-plugins \
+              --disable-docbook \
+              --with-x --with-x11 --with-term --with-sdl2) || exit
+
+make && make install

scripts/gcc-build.sh

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+#! /usr/bin/bash
+sudo apt update &&\
+     sudo apt install -y \
+		build-essential \
+		bison\
+		flex\
+		libgmp3-dev\
+		libmpc-dev\
+		libmpfr-dev\
+		texinfo
+
+BINUTIL_VERSION=2.37
+BINUTIL_URL=https://ftp.gnu.org/gnu/binutils/binutils-2.37.tar.xz
+
+GCC_VERSION=11.2.0
+GCC_URL=https://ftp.gnu.org/gnu/gcc/gcc-11.2.0/gcc-11.2.0.tar.xz
+
+GCC_SRC="gcc-${GCC_VERSION}"
+BINUTIL_SRC="binutils-${BINUTIL_VERSION}"
+
+# download gcc & binutil src code
+
+export PREFIX="$HOME/cross-compiler"
+export TARGET=i686-elf
+export PATH="$PREFIX/bin:$PATH"
+
+mkdir -p "${PREFIX}"
+mkdir -p "${HOME}/toolchain/binutils-build"
+mkdir -p "${HOME}/toolchain/gcc-build"
+
+cd "${HOME}/toolchain"
+
+if [ ! -d "${HOME}/toolchain/${GCC_SRC}" ]
+then
+	(wget -O "${GCC_SRC}.tar" ${GCC_URL} \
+		&& tar -xf "${GCC_SRC}.tar") || exit
+	rm -f "${GCC_SRC}.tar"
+else
+	echo "skip downloading gcc"
+fi
+
+if [ ! -d "${HOME}/toolchain/${BINUTIL_SRC}" ]
+then
+	(wget -O "${BINUTIL_SRC}.tar" ${BINUTIL_URL} \
+		&& tar -xf "${BINUTIL_SRC}.tar") || exit
+	rm -f "${BINUTIL_SRC}.tar"
+else
+	echo "skip downloading binutils"
+fi
+
+echo "Building binutils"
+
+cd "${HOME}/toolchain/binutils-build"
+
+("${HOME}/toolchain/${BINUTIL_SRC}/configure" --target=$TARGET --prefix="$PREFIX" \
+	--with-sysroot --disable-nls --disable-werror) || exit
+
+(make && make install) || exit
+
+echo "Binutils build successfully!"
+
+echo "Building GCC"
+
+cd "${HOME}/toolchain/gcc-build"
+
+which -- "$TARGET-as" || echo "$TARGET-as is not in the PATH"
+
+("${HOME}/toolchain/${GCC_SRC}/configure" --target=$TARGET --prefix="$PREFIX" \
+	--disable-nls --enable-languages=c,c++ --without-headers) || exit
+
+(make all-gcc &&\
+ make all-target-libgcc &&\
+ make install-gcc &&\
+ make install-target-libgcc) || exit
+
+echo "done"