Add background on license choice

[fkohrt]

As this also came up in the feedback: What are the pros and cons of the licenses recommended in this tutorial, and how do they compare to other common licenses (in particular, MIT)?

For example, choosing CC0 avoids a lot of the hassle around what constitutes a derivative work:

• When I use CC BY-SA media in a website, do I "remix, transform, or build upon the material"?
• Extent of adapted material "contagion" in Wikipedia style CC BY-SA licenses
• Understanding 'Adapted Material' for illustrations in a book
• Using CC BY-SA music in a podcast