Add explicit license of Waffle binary library to ARM subfolder.

Waffle's license and its use by us is already mentioned/contained
in our master License.txt file, but place a copy of libWaffle's
license also in Psychtoolbox/PsychContributed/ARMArch/ subfolder,
where the prebuilt binary libwaffle.so for Nexus-7/Tegra-3/ARM SoC
is stored.