Update Flashing_eMMC.rst for changes in librem-flash-image behaviour
The current documentation leads people (me at least) astray; arguably made worse by the fact that librem5-devkit-flash-image still exists but does not do what it says on the tin.
The current documentation leads people (me at least) astray; arguably made worse by the fact that librem5-devkit-flash-image still exists but does not do what it says on the tin.