Update Build Documentation for Windows

Since the addition of the custom font #295, the Windows build instructions are not correct and will not work due to the addition of python and the python library pillow.

The Windows build instructions uses MSys2 to host the Devkitpro toolchains/libraries. It uses pacman for package management, as per the Devkitpro instructions. pacman can also be used to install the python and python-pillow libraries required to compile the project.

Currently, there is this unclean solution:

# First, add the mirror to get the python libraries. This should only be ran to prevent
# multiple entries
echo -e "[mingw64]\nServer = https://mirror.msys2.org/mingw/mingw64" >> /etc/pacman.conf
# Update pacman references and packages
pacman -Syu --noconfirm
# Install python-pillow from the mirror, note this installs python as a dependency
pacman -S --noconfirm mingw-w64-x86_64-python-pillow
# Add the path of the new binary to your shell.
echo "export PATH="/mingw64/bin:$PATH"" >> /etc/bash.bashrc
# Refresh your bash session with the new PATH
source /etc/bash.bashrc

This needs to be refined and documented. "Refined" being removed of the bugs mentioned in the comments and configured to be easily ran multiple times.

Reference issue: #376