include a copy of the CC-BY 3.0 License that the docs are under

downloaded from http://creativecommons.org/licenses/by/3.0/legalcode.txt
Merge pull request #10693 from twbs/include-docs-license

include a copy of the CC-BY 3.0 License that the docs are under
@headingsColor → @headings-color
Merge pull request #10749 from ZDroid/patch-2

@headingsColor → @headings-color