Add explanatory language about the "a-format" files

[mtmccrea]

From @elifieldsteel's recent PR (#5)

It may be helpful if specific information about files in the "b-format" folder were included in the README file (specifically to do with Ambisonic order, component ordering, normalization, and encoding radius), to make the converting/decoding process as unambiguous as possible. Some language is suggested in this PR as a starting point, feel free to reword it, move it elsewhere in the README, etc.

These changes were merged, but still TODO:

It might also be appropriate to add similar language about the "a-format" files, since there may be even more ambiguity here regarding the tetrahedral orientation and conversion/decoding process. Proposed language for these files is not included here, because I'm not fully aware of these specific details.

[joslloand]

It would be a good idea to add to README and/or LICENSE info and links to where the various files are referenced in the atk-sc3's FOA tutorial pages.

• https://depts.washington.edu/dxscdoc/Help/Guides/Intro-FOA-Examples.html#Produced%20via%20the%20Ambisonic%20Toolkit
• https://depts.washington.edu/dxscdoc/Help/Guides/Intro-FOA-Examples.html#Natural%20soundfields,%20with%20imaging%20transforms
• https://depts.washington.edu/dxscdoc/Help/Guides/Encoding-FOA.html#Stereo%20matrix
• https://depts.washington.edu/dxscdoc/Help/Guides/Encoding-FOA.html#Super%20Stereo
• https://depts.washington.edu/dxscdoc/Help/Guides/Encoding-FOA.html#Ambisonic%20UHJ%20stereo
• https://depts.washington.edu/dxscdoc/Help/Guides/Encoding-FOA.html#Octophonic
• https://depts.washington.edu/dxscdoc/Help/Guides/Encoding-FOA.html#Dome
• https://depts.washington.edu/dxscdoc/Help/Guides/Encoding-FOA.html#Spaced%20microphones
• https://depts.washington.edu/dxscdoc/Help/Guides/Encoding-FOA.html#ZoomH2,%20forward
• https://depts.washington.edu/dxscdoc/Help/Guides/Encoding-FOA.html#ZoomH2,%20reversed