[Feature] Add in FAQ: using music samples released under the CC BY-SA

## Problem
Recently, on the web, there's been some discussion about compliance with the CC BY-SA in the case of music samples.

This discussion sprung from [this post](http://virtualplaying.com/virtual-playing-orchestra/comment-page-3/#comment-703) (and [related video](https://www.youtube.com/watch?v=xvowEZqgflw)) by popular libre software vlogger @unfa and initially concerned the [Virtual Playing Orchestra](http://virtualplaying.com/virtual-playing-orchestra/#license-screencaps).

This, I think, can be attributed to the lack of information specific to music samples in the [official CC FAQ](https://creativecommons.org/faq/).

## Description
Explicitly addressing usage of CC BY-SA music samples in songs would dispel any confusion surround the issue, answering these questions:

**Does the sharealike clause (i) only apply to strictly derivative works in the same domain (e.g. other samples or music libraries based on samples released under the CC BY-SA) or (ii) does it apply to the songs which incorporate said samples (e.g. using a single sample released under the CC BY-SA in a song makes all the song under the CC BY-SA)?**

**If (i) is true, is attribution the only requirement for license compliance in songs incorporating samples released under the CC BY-SA?**

**Else, if (ii) is true, does the CC BY-SA extend to the composition as well? (e.g. using a single sample licensed under the CC BY-SA in a song gives users the right to cover that song, even if the sample has nothing to do with the composition)**

Since samples released under both the CC BY-SA 3.0 and 4.0 are available, if there are any significant differences between the two, that should be addressed as well.