Add a method to properly remove TermuxArch from device

[Harshiv-Patel]

I could have just did rm -rf but I feel that you should add little script that can remove TermuxArch from device in proper way, or add something in wiki section about how to do it in proper way.

[SDRausty]

@Harshiv-Patel https://github.com/sdrausty/TermuxArch/blob/master/scripts/debug/sraf.sh purges the install from device.

[SDRausty]

A new method has just been added with commit 18ae664 Use bash setupTermuxArch.sh uninstall to purge your Arch Linux installation from device. This will remove $PREFIX/bin/startarch if created, and $HOME/arch.