Uninstall TXM instructions

Add a section to guide users who wish to uninstall TXM (?????????????)

Instructions :

• Windows : run TXM uninstaller from the Start menu
• Mac OS X :
  • from Finder : delete the "/Applications/TXM-X.Y.Z" app
  • from the terminal : sudo rm -rf /Applications/TXM-X.Y.Z.app
• Ubuntu :
  • from the logitheque
    • open the logitheque, search for "txm" ou open a TXM deb file
    • select "delete/supprimer"
  • from terminal : sudo apt remove txm-x.y.z

also add details to completely remove TXM working files (= remove the HOME/TXM-X.Y.Z and HOME/.TXM-X.Y.Z directories) ?